Collision Theory Reversible Chemical Reactions BIOB111 CHEMISTRY & BIOCHEMISTRY Session 4
Key concepts: session 4 From this session you are expected to develop an understanding of the following concepts: Concept 1: Processes that occur during a chemical reaction Concept 2: Collisions to begin chemical reactions Concept 3: Changing the rate of a chemical reaction Concept 4: Energy transfer in chemical reactions Concept 5: Activation energy Concept 6: Endothermic reactions Concept 7: Exothermic reactions Concept 8: Equilibrium reactions Concept 9: Stresses on equilibrium reactions These concepts are covered in the Conceptual multiple choice questions of tutorial 4
Session Overview Part 1: Molecular collisions Chemical equations represent chemical reactions Collisions between molecules drive chemical reactions Part 2: Interpreting chemical reactions Chemical reaction rate Energy transfer in chemical reactions Exothermic vs endothermic reactions Part 3: Chemical equilibrium Chemical equilibrium Re-establishing chemical equilibrium
Part 1: Molecular collisions Chemical equations represent chemical reactions Collisions between molecules drive chemical reactions
Chemical equations represent chemical reactions Progression through a chemical reaction: Start- step 1: The chemical bonds holding the reactant molecules together are broken Chemical bond breakage requires an energy input Example below: Chemical bonds broken within methane and oxygen Middle- step 2: Once the chemical bonds have been broken, the atoms rearrange to adopt new positions Example below: Carbon, hydrogen and oxygen atoms rearrange End- step 3: After atom rearrangement, new chemical bonds form between the atoms creating the products Chemical bond formation releases energy Example below: New chemical bonds are formed to produce carbon dioxide and water Chemical reaction: Reactant 1 Reactant 2 Product 1 Product 2
Chemical equations represent chemical reactions H Reactant 1: Methane Reactant 2: Oxygen Product 1: H C H H O O + + C O O Carbon dioxide O O H H Product 2: water O O H H
Chemical equations represent chemical reactions Start- step 1: Chemical bond breakage in reactants H Reactant 1: Methane Reactant 2: Oxygen H C H H + O O O O Covalent bond broken Bond breakage requires energy
Chemical equations represent chemical reactions Middle- step 2: Atom rearrangement H H C H H + O O O O
Chemical equations represent chemical reactions End- step 3: Chemical bond formation in products Product 2: Water O H H Newly formed covalent bond Bond formation releases energy O H H Product 2: Water Product 1: Carbon dioxide C O O
Chemical equations represent chemical reactions 1(CH 4 ) + 2(O 2 ) 1(CO 2 ) + 2(H 2 O) CH + 4 2O 2 CO + 2 2H 2 O Simplified representation
Collisions between molecules drive chemical reactions Collisions between different molecules drive chemical reactions Different reactant molecules must collide to form products Most collisions do not result in a chemical reaction, as the molecules just bounce off each other Only effective collisions allow the chemical reaction to begin http://phet.colorado.edu/en/simulation/legacy/reactions-and-rates
Collisions between molecules drive chemical reactions Only effective collisions result in a chemical reaction NO 2 + CO NO + CO 2 An effective collision requires: 1) Convenient orientation of molecules at the time of collision 2) The energy of the Collision must meet the activation energy The collision between molecules must have sufficient energy to break specific chemical bonds within the reactants The energy of a collision depends on the speed of reactant molecules and on the angle of their approach Activation Energy: The minimum amount of energy from the collision between two reactant molecules that will allow the chemical reaction to begin
Collisions between molecules drive chemical reactions Effective collision High energy collision, which meets the activation energy Collision has a convenient orientation with the carbon (from CO) and the oxygen (from NO 2 ) colliding N N O O O O C O C O NO 2 + CO NO + CO 2
Collisions between molecules drive chemical reactions Unsuccessful collision Collision has an inconvenient orientation with the carbon (from CO) and the nitrogen (from NO 2 ) colliding O O N O O N C O C O NO 2 + CO NO + CO 2
Collisions between molecules drive chemical reactions Unsuccessful collision Collision has a convenient orientation with the carbon (from CO) and the oxygen (from NO 2 ) colliding Low energy collision, which does not meet the activation energy N N O O O O C O C O NO 2 + CO NO + CO 2
NO + O 3 NO 2 + O 2 When reactant molecules (above) collide, what factors determine whether a chemical reaction will occur? G
NO + O 3 NO 2 + O 2 When reactant molecules (above) collide, what factors determine whether a chemical reaction will occur? For the chemical reaction to take place, the energy of the collision (between the reactant molecules) must be equal to or greater than the activation energy Collision energy activation energy: Collision energy allows specific chemical bonds within the reactants to be broken Atoms rearranged Products formed (new chemical bonds formed) The angle that NO and O 3 collide must be convenient Oxygen must collide with nitrogen, to allow an extra oxygen to bond to nitrogen (after detaching from O 3 )
Attempt Socrative questions: 1 to 4 Google Socrative and go to the student login Room name: City name followed by 1 or 2 (e.g. PERTH1) 1 for 1 st session of the week and 2 for 2 nd session of the week
Part 1: Molecular collisions Chemical equations represent chemical reactions In a chemical reaction, the reactants on the left hand side are converted into the products on the right hand side of the equation, with the arrow representing the progression of the chemical reaction CH 4 + 2O 2 CO 2 + 2H 2 O No atoms are created or destroyed in a chemical reaction, only rearranged to form new substances (products) Collisions between molecules drive chemical reactions Collisions between reactant molecules provide the energy required to begin the chemical reaction For a collision to allow a chemical reaction to begin, the collision must: Have a collision energy equal to or greater than the activation energy Required to break some of the chemical bonds that exist within the reactants Have a convenient orientation between the colliding reactants, which allows specific chemical bonds to be broken to start the chemical reaction
Part 2: Interpreting chemical reactions Chemical reaction rate Energy transfer in chemical reactions Exothermic vs endothermic reactions
Chemical reaction rate Reaction Rate: The rate at which reactants are converted into products in a chemical reaction in a given time period Tracking how often the chemical reaction occurs NO 2 + CO NO + CO 2 Reactants Products
Chemical reaction rate How can the rate of a chemical reaction be determined? 2 different ways: Determine how much product is being formed in a given period of time Determine how much reactant is being used up (consumed) in a given period of time
Chemical reaction rate Establishing the rate of a chemical reaction by tracking the amount of product being created 2H 2 O 2 2H 2 O + O 2 Hydrogen peroxide (liquid) Water (liquid) Oxygen (gas) Chemical reaction rate = Change in concentration (amount) of product or reactant Time Evidence that the chemical reaction has taken place is the creation of the oxygen gas (product) For example, if 600 ml of oxygen is produced in 7 minutes Reaction rate = 85.7 ml of oxygen produced per minute (or 1.43 ml per second)
Chemical reaction rate Establishing the rate of a chemical reaction by tracking the amount of reactant being used up 2C 2 H 5 OH + 3O 2 3H 2 O + CO 2 Ethanol (liquid) Oxygen (gas) Water vapour (gas) Carbon dioxide (gas) Chemical reaction rate = Change in concentration (amount) of product or reactant Time Evidence that the chemical reaction has taken place is the decrease in the amount of ethanol present (reactant) For example, if 200 ml of ethanol is used up (combusted/burnt) in 70 minutes Reaction rate = 2.9 ml of ethanol consumed per minute (or 0.05 ml per second)
Chemical reaction rate Two main factors affect the rate of a chemical reaction: How often collisions occur between the reactant molecules The speed of the collisions between the reactant molecules The higher the speed of the reactant molecules, the larger the collision energy High collision energies are likely to meet the activation energy N N O O O O C O C O Effective collision Collision which meets the activation energy Collision has a convenient orientation with the carbon (from CO) and the oxygen (from NO 2 ) colliding
Chemical reaction rate The factors below have affect one or both of: The number of collisions between reactant molecules The energy of the collisions between reactant molecules Amount (concentration) of reactant molecules present Reaction rate increases as concentration increases Increased rate of collisions between molecules Temperature Reaction rate increases as temperature increases Increased rate of collisions The energy of the molecular collisions increases, as the reactant molecules are moving more quickly Catalysts Catalysts lower the activation energy Energy needed from the molecular collisions to begin the chemical reaction decreases Catalysts are not consumed in the reaction Catalysts can be reused in future chemical reactions Physical state of the reactant molecules Chemical reactions occur faster between reactants in the same physical state Gas-gas interaction are the fastest Allows for highest rate of molecular collisions
Chemical reaction rate Amount (concentration) of reactant molecules present Reaction rate increases as concentration increases Increased rate of collisions between molecules Low reactant concentration High reactant concentration Reactant Concentration Increasing the concentration of one or more types of reactant molecules: Increases the amount of collisions between reactant molecules Effective collisions occurs more frequently, which increases the reaction rate http://phet.colorado.edu/en/simulation/legacy/reactions-and-rates
Chemical reaction rate Temperature High temperatures increase the rate of the chemical reaction Molecules move faster & collide more frequently The reaction rate doubles for every 10ᵒC increase in temperature Low temperature decrease the rate of the chemical reaction Molecules move more slowly & collide less frequently Temperature Reaction rate increases as temperature increases Increased rate of collisions The energy of the molecular collisions increases, as the reactant molecules are moving more quickly Normal body temperature: 36.5 and 37.4ᵒC Increasing the body temperature causes: An increase in the rate of the biochemical reactions that occur in the body An increase in both the breathing and heart rate Hyperthermia: Core body temperature above 41ᵒC Rate of biochemical reaction rate increases Hypothermia: Core body temperature below 36ᵒC Rate of biochemical reaction rate decreases
Chemical reaction rate High temperature: 40 C Effective collision High energy collision, which meets the activation energy Collision has a convenient orientation with the carbon (from CO) and the oxygen (from NO 2 ) colliding N N O O O O C O C O NO 2 + CO NO + CO 2
Chemical reaction rate Low temperature: 5 C Unsuccessful collision Collision has a convenient orientation with the carbon (from CO) and the oxygen (from NO 2 ) colliding Low energy collision, which does not meet the activation energy N N O O O O C O C O NO 2 + CO NO + CO 2
Chemical reaction rate Catalysts Catalysts lower the activation energy Energy needed from the molecular collisions to begin the chemical reaction decreases Catalysts are not consumed in the reaction Catalysts can be reused in future chemical reactions Catalyst: A substance that increases the reaction rate without being consumed in the chemical reaction A specific catalyst lowers the activation energy of a specific chemical reaction Due to the lower activation energy, more molecular collisions between reactants will be successful Increases the reaction rate Stoker 2014, Figure 9-10 p251
Chemical reaction rate NO + O 3 NO 2 + O 2 No catalyst Energy units 100 50 1 effective collision Activation energy Activation energy required for the above reaction to proceed is 90 units of energy Activation energy with catalyst present is 70 energy units Lower activation energy due to the presence of the catalyst 3 different molecular collisions occur between NO + O 3 : C1: 100 units of energy from collision C2: 80 units of energy from collision C3: 50 units of energy from collision Catalyst present Energy units 0 100 50 0 C1 C1 C2 C3 Collisions C2 C3 Collisions 2 unsuccessful collisions 2 effective collisions Lower activation energy 1 unsuccessful collision
Chemical reaction rate Enzymes are the catalysts of the human body: Enzymes allow chemical reactions in the body to occur quickly enough to keep us alive All enzymes are proteins Specific enzymes decrease the amount of energy required to begin specific chemical reactions Decrease the activation energy Timberlake 2014, Figure 3, p.737
Energy transfer in chemical reactions Progression through a chemical reaction: Start- step 1: The chemical bonds holding the reactants together are broken Chemical bond breakage requires an energy input Example below: Chemical bonds broken within methane and oxygen Middle- step 2: Once the chemical bonds have been broken, the atoms rearrange to adopt new positions Example below: Carbon, hydrogen and oxygen atoms rearrange End- step 3: After atom rearrangement, new chemical bonds form between the atoms creating the products Chemical bond formation releases energy Example below: New chemical bonds are formed to produce carbon dioxide and water Chemical reactions include breaking of old chemical bonds (in the reactants) & the formation of new chemical bonds (in the products) Overall, a chemical reaction can either release or absorb energy, depending on the reaction
Energy transfer in chemical reactions Activation Energy: The minimum amount of energy from the collision between two reactant molecules that will allow the chemical reaction to begin Energy units 200 100 0 Few effective collisions Collisions High Activation energy Many unsuccessful collisions A chemical reaction with a high activation energy: A large amount of energy input is needed to begin the chemical reaction Few collisions between reactant molecules meet the activation energy = the chemical reaction proceeds at a slow rate Chemical reaction with a high activation energy of 150 energy units Most collisions will be unsuccessful, as the energy of the molecular collisions will frequently be below the activation energy Few chemical reactions take place
Energy transfer in chemical reactions Activation Energy: The minimum amount of energy from the collision between two reactant molecules that will allow the chemical reaction to begin Energy units 200 100 Few unsuccessful collisions 0 Many effective collisions Collisions Low Activation energy A chemical reaction with a low activation energy: A small amount of energy input is needed to begin the chemical reaction A large amount of collisions between reactant molecules meet the activation energy = the chemical reaction proceeds at a fast rate Chemical reaction with a low activation energy of 50 energy units Most collisions will be effective (successful), as the energy of the collision will frequently be above the activation energy Many chemical reactions take place
Energy transfer in chemical reactions High activation energy chemical reaction Low activation energy chemical reaction Energy units 200 100 0 Few effective collisions Collisions High Activation energy Many unsuccessful collisions Energy units 200 100 Few unsuccessful collisions 0 Many effective collisions Collisions Low Activation energy Few effective collisions = few chemical reactions Many effective collisions = Many chemical reactions
https://www.freeimages.com/photo/leaf-detail-1153686 https://www.freeimages.com/photo/blue-flame-1402795 Exothermic vs endothermic reactions Exothermic reaction Wax candle burning (combustion reaction) Exothermic reactions release energy Endothermic reaction Photosynthesis (makes glucose) Endothermic reactions absorb (require) energy 2C 22 H 46 (wax) + 67O 2 44CO 2 + 46H 2 O + energy 6CO 2 + 6H 2 O + energy C 6 H 12 O 6 (glucose) + 6O 2
Exothermic vs endothermic reactions Exothermic chemical reactions Overall, energy is released by the reaction Low amount of energy needed to start the reaction (low activation energy) = high rate of reaction (occurs readily) Energy seen on the product side of the reaction (energy produced) Endothermic chemical reactions Overall, energy is absorbed by the reaction High amount of energy needed to start the reaction (high activation energy) = low rate of reaction (occurs slowly) Energy seen on the reactant side of the reaction (energy consumed)
Exothermic vs endothermic reactions Exothermic Reaction Exothermic reactions release energy (often in the form of heat) The products of an exothermic reaction contain less energy than the reactants Example: 3H 2 +N 2 2NH 3 + 22.0 kcal energy Stoker 2014, Figure 9.7, p248
Exothermic vs endothermic reactions Endothermic Reaction Endothermic reactions absorb energy The products of an endothermic reaction contain more energy than the reactants Example: H 2 O + 137 kcal energy 2H 2 + O 2 Stoker 2014, Figure 9.7, p248
Key concept: chemical reactions, activation energy Is a chemical reaction with a high or low activation energy more likely to take place? Why? For a chemical reaction with a high activation energy, will the reactants be converted into products readily or slowly? Explain. For a chemical reaction with a low activation energy, is more energy released or consumed overall by the reaction? Explain.
Attempt Socrative questions: 5 to 9 Google Socrative and go to the student login Room name: City name followed by 1 or 2 (e.g. PERTH1) 1 for 1 st session of the week and 2 for 2 nd session of the week
Part 2: Interpreting chemical reactions Chemical reaction rate The chemical reaction rate is the speed that reactants are converted into products Chemical reaction rate can be determined by: Tracking the number of products created in a specific time period Tracking the number of reactants used up in a specific time period The rate of a chemical reaction is largely determined by: The number of collisions between the reactant molecules The speed of the collisions between the reactant molecules Other factors that affect chemical reaction rate: Temperature Amount (concentration) of reactant molecules Presence or absence of a catalyst Physical state (solid, liquid or gas) of the reactant molecules
Part 2: Interpreting chemical reactions Energy transfer in chemical reactions To begin a chemical reaction, an energy input is required to break some of the existing chemical bonds present in the reactants The energy input is the activation energy After atom rearrangement, new chemical bonds are formed in the products, which releases energy The activation energy is the minimum amount of energy from the collision between two reactant molecules that will allow the chemical reaction to begin If a molecular collision exceeds (or is equal to) the activation energy, the chemical reaction begins If a molecular collision is lower than the activation energy, no chemical reaction occurs Chemical reactions with a high activation energy, require a large energy input Few molecular collisions meet the activation energy, resulting in a low reaction rate Chemical reactions with a low activation energy, require a small energy input Many molecular collisions meet the activation energy, resulting in a high reaction rate
Part 2: Interpreting chemical reactions Exothermic vs endothermic reactions Exothermic reactions are those that overall release energy Energy is one of the products Exothermic reactions have low activation energies and high reaction rates Example: Combustion reactions: burning a wax candle Endothermic reactions are those that overall consume energy Energy is one of the reactants Endothermic reactions have high activation energies and low reaction rates Example: Photosynthesis: where energy is consume to make the energy rich glucose
Part 3: Chemical equilibrium Reversible vs non-reversible chemical reactions Chemical equilibrium Re-establishing chemical equilibrium Biologically relevant reversible reaction
Reversible vs non-reversible chemical reactions Reversible chemical reactions can proceed in both the forward and reverse directions Shown by a double arrow N 2 + 3H 2 2NH 3 Non-reversible chemical reactions proceed in the forward direction only Shown by a single arrow CH 4 + 2O 2 CO 2 + 2H 2 O
Chemical equilibrium Chemical equilibrium: A chemical equilibrium is achieved when the forward and reverse reactions occur at the same rate Once a chemical equilibrium is established: The rate of the forward reaction = the rate of the reverse reaction The concentrations (amounts) of reactants & products do not change As quickly as the products are made via the forward reaction, other product molecules are converted back into reactants via the reverse reaction A chemical equilibrium is dynamic Both forward and reverse reactions are occurring at the same time Neither reaction stops during a chemical equilibrium N 2 + 3H 2 2NH 3 N N H H H H H H H H H N H N H H
Reversible chemical reaction at equilibrium The amount of ammonia, hydrogen and nitrogen created = the amount of ammonia, hydrogen and nitrogen consumed N 2 + 3H 2 2NH 3 Forward reaction: N 2 + 3H 2 2NH 3 Reverse reaction: 2NH 3 N 2 + 3H 2 Nitrogen and hydrogen used to make ammonia (2NH 3 ) Amount of nitrogen and hydrogen decreases Amount of ammonia increases Ammonia (2NH 3 ) used to make nitrogen and hydrogen Amount of ammonia decreases Amount of nitrogen and hydrogen increases
Reversible chemical reaction at equilibrium The amount of ammonia, hydrogen and nitrogen created = the amount of ammonia, hydrogen and nitrogen consumed N 2 + 3H 2 2NH 3 Once a chemical equilibrium is established: The rate of the forward reaction = the rate of the reverse reaction The concentrations (amounts) of N 2, H 2 (reactants) and NH 3 (product) do not change As quickly as the NH 3 molecules are made via the forward reaction, other NH 3 molecules are broken down into N 2 and H 2 molecules via the reverse reaction
Re-establishing chemical equilibrium Equilibrium is not permanent for a reversible chemical reaction Equilibrium can be lost due to a stress Examples of stresses: Change in the amount of one or more of the reactant or product molecules Change in temperature
Re-establishing chemical equilibrium Once a stress is applied to a chemical reaction at equilibrium: According to Le Châtelier s Principle: the chemical reaction adjusts to remove the stress in order to re-establish equilibrium Ways that a chemical reaction can adjust to a stress: Increase the rate of the forward reaction Increase the rate of the backward reaction
Re-establishing chemical equilibrium N 2 + 3H 2 2NH 3 The above chemical reaction is at equilibrium until a stress pushes the reaction out of equilibrium Stress applied: adding more NH 3 (product) What is the best way for the chemical reaction to remove the stress and re-establish equilibrium? Remove the added NH 3 (product) by increasing the rate of the reverse reaction More NH 3 (product) will be broken down into the N 2 + 3H 2 reactants Once enough of the added NH 3 has been broken down via the reverse reaction, the rates of the forward and reverse reactions will return to the same rate and equilibrium will be re-established
Re-establishing chemical equilibrium N 2 + 3H 2 2NH 3 The above chemical reaction is at equilibrium until a stress pushes the reaction out of equilibrium Stress applied is the adding more H 2 (reactant) What is the best way for the chemical reaction to remove the stress and re-establish equilibrium? Remove the added H 2 (reactant) by increasing the rate of the forward reaction More H 2 (reactant) (and N 2 ) and will be converted into the NH 3 product Once enough of the added H 2 has been converted to NH 3 via the forward reaction, the rates of the forward and reverse reactions will return to the same rate and equilibrium will be re-established
Re-establishing chemical equilibrium N 2 + 3H 2 2NH 3 The above chemical reaction is at equilibrium until a stress pushes the reaction out of equilibrium Stress applied is the removal of N 2 (reactants) What is the best way for the chemical reaction to remove the stress and re-establish equilibrium? Increase the amount of N 2 by increasing the rate of the reverse reaction More N 2 (reactant) will be created, by breaking down the NH 3 product into the N 2 and H 2 reactants Once enough of the NH 3 has been broken down into N 2 and H 2 via the reverse reaction, the rates of the forward and reverse reactions will return to the same rate and equilibrium will be re-established
Biologically relevant reversible reaction The haemoglobin (Hb) protein in our blood can bind to either oxygen or carbon monoxide (CO) in the reversible chemical reaction shown below Hb(O 2 ) 4 + 4CO Hb(CO) 4 + 4O 2 O 2 O 2 O 2 O 2 CO CO CO CO CO CO CO CO O 2 O 2 O 2 O2 O 2 CO Haemoglobin Oxygen molecule Carbon monoxide compound The chemical bonds that attach haemoglobin to CO are 300 times stronger than between haemoglobin and O 2 The reversible reaction favours the right-hand side, meaning more haemoglobin bind CO than O 2 Once haemoglobin binds CO, it is not available to bind to O 2 Hb(CO) 4 is even more red than haemoglobin with oxygen bound Can show as a red flushed face
Biologically relevant reversible reaction The haemoglobin (Hb) protein in our blood can bind to either oxygen or carbon monoxide (CO) in the reversible chemical reaction shown below Hb(O 2 ) 4 + 4CO Hb(CO) 4 + 4O 2 O 2 O 2 O 2 O 2 CO CO CO CO CO CO CO CO O 2 O 2 O 2 O2 O 2 CO Haemoglobin Oxygen molecule Carbon monoxide compound To treat carbon monoxide poisoning, the reversible reaction must be shifted to the left to allow haemoglobin to bind to oxygen Increasing the O 2 will shift the reversible reaction to the left, to use up the excess oxygen Oxygen will bind to haemoglobin instead of carbon monoxide CO can be exhaled
N 2 + 3H 2 2NH 3 Key concept: equilibrium, forward and reverse reactions With reference to the rate of the forward and reverse chemical reactions, what is a chemical equilibrium? What may disrupt a chemical equilibrium? Why would the factor you have identified disrupt the chemical equilibrium? In the above reaction, would the addition of more product (NH 3 ) increase the rate of the forward or reverse reaction? Why?
Attempt Socrative questions: 10 and 11 Google Socrative and go to the student login Room name: City name followed by 1 or 2 (e.g. PERTH1) 1 for 1 st session of the week and 2 for 2 nd session of the week
Part 3: Chemical equilibrium Reversible vs non-reversible chemical reactions Reversible reactions can proceed in either the forward or reverse direction Shown by a double-headed arrow Non-reversible reactions can proceed in only the forward direction Shown by a single-headed arrow Chemical equilibrium Chemical equilibrium occurs when the rate of the forwards and reverse reactions are equal (in a reversible reaction) Both the forward and the reverse reactions are occurring at equilibrium Once equilibrium is established, the concentration (amount) of the reactants and products does not change
Part 3: Chemical equilibrium Re-establishing chemical equilibrium Equilibrium is not permanent and chemical reactions can be pushed out of equilibrium by stresses such as: Change to the amount of a specific reactant or product molecule Change in temperature According to Le Châtelier s Principle, the chemical reaction adjusts to remove the stress in order to re-establish equilibrium by either: Increasing the rate of the forward reaction Increasing the rate of the backward reaction The reversible reaction attempts to return to equilibrium by accelerating either the forward or the reverse reaction, to remove the added stress Biologically relevant reversible reaction Haemoglobin binds to either oxygen or carbon monoxide in a reversible reaction By adding extra oxygen molecules, the haemoglobin is forced to attach to oxygen in preference to carbon monoxide
Readings & Resources Stoker, HS 2014, General, Organic and Biological Chemistry, 7 th edn, Brooks/Cole, Cengage Learning, Belmont, CA. Stoker, HS 2004, General, Organic and Biological Chemistry, 3 rd edn, Houghton Mifflin, Boston, MA. Timberlake, KC 2013, General, organic, and biological chemistry: structures of life, 4 th edn, Pearson, Boston, MA. Alberts, B, Johnson, A, Lewis, J, Raff, M, Roberts, K & Walter P 2008, Molecular biology of the cell, 5 th edn, Garland Science, New York. Berg, JM, Tymoczko, JL & Stryer, L 2012, Biochemistry, 7 th edn, W.H. Freeman, New York. Dominiczak, MH 2007, Flesh and bones of metabolism, Elsevier Mosby, Edinburgh. Tortora, GJ & Derrickson, B 2014, Principles of Anatomy and Physiology, 14 th edn, John Wiley & Sons, Hoboken, NJ. Tortora, GJ & Grabowski, SR 2003, Principles of Anatomy and Physiology, 10 th edn, John Wiley & Sons, New York, NY.