Warm up 1) What is the conjugate acid of NH 3? 2) What is the conjugate base of HNO 2? 3) If the ph is 9.2, what is the [H 3 O + ], poh, and [OH - ]? 4) What is the concentration of H 2 SO 4 if 30.1 ml of it is titrated with 41.22 ml of 0.50M NaOH
Test Topics Acid/Base Reactions Arrhenius vs. Bronsted-Lowery Strong acids and bases Strong vs. Concentrated Uses of common acids Conjugate acids and bases ph and poh calculations Titration concepts and calculations Solutions stuff
Intro to Thermodynamics Almost all chemical reactions involve a change in energy (usually in the form of heat) Thermo Dynamics
Energy Energy- is the ability to do work or produce heat Heat is the transfer of energy between two objects of different temperatures
Thermodynamics Thermochemistry- is the study of heat change that accompany chemical reaction and phase changes. Heat absorbed: Heat released:
Endothermic / Exothermic Endothermic heat/energy must be added for a reaction. Exothermic heat/energy are released from the reaction.
Thermodynamics Heat (q) flows from hot to cold * Measured in joules (J) which is the SI unit of heat energy as well as all other forms of energy Other units: kj, cal, Cal
Conversions 1000 J = 1 kj 1 calorie = 4.184J 1000 cal = 1 Cal (food calorie)
Practice Problem A fruit and oatmeal bar contains 142 Calories. Convert this energy to joules.
Thermodynamics Temperature: A measure of the average kinetic energy of the atoms or molecules of substance A measure of hotness or coldness of an object Units: Celsius, Kelvin and Fahrenheit
Difference between Heat and Temperature Heat is the transfer of thermal energy from a higher temperature to a lower temperature Thermal (heat) energy: the sum total of the kinetic energies of the particles in the sample of matter. Measured in Joules (J)
Temperature continued Temperature measures the AVERAGE kinetic energy The faster the molecules are moving The slower the molecules are moving
Temp vs. Heat Heat flows from hot to cold Compare and contrast temperature and thermal energy of the Pacific Ocean to a boiling pot of water
Warm Up 1) A Double Quarter Pounder in Cheese at a McDonald s is 750 Calories of stored energy, how much energy in joules will it supply? 2) Write the chemical formula that forms when Nitrite and Magnesium bond 3) Which element has a higher ionization energy? Calcium (Ca) or Gallium (Ga)
Enthalpy Enthalpy (H) the heat content of a system Heat of reaction (ΔH): The quantity of heat released or absorbed during a reaction ΔH = H products - H reactants
ΔH Each reaction will have an enthalpy change which indicates whether the reaction is endothermic or exothermic.
The sign of the enthalpy of reaction: If ΔH is negative then heat is being released and the reaction is exothermic If ΔH is positive then heat is being absorbed and the reaction is endothermic To determine if the reaction is exothermic or endothermic, you must know the value of ΔH
Endothermic vs. Exothermic
Example Rewrite the following equation including the ΔH value as a reactant or product and indicate if it is exothermic or endothermic H 2 + ½ O 2 H 2 O ΔH = -241.8 kj
You try it! Rewrite the following equation including the ΔH value as a reactant or product and indicate if it is exothermic or endothermic H 2 O H 2 + ½ O 2 ΔH = 241.8 kj
Enthalpy ΔH is an extrinsic physical property because it depends on the amount present! Determine the ΔH for the following reactions: N 2 + 3H 2 2NH 3 H= -91.8 kj ½ N 2 + 3/2 H 2 NH 3 H = kj 2NH 3 N 2 + 3H 2 H = kj
Phase Changes Phase change is the change of state of a substance (solid, liquid, or gas) To change phases, heat must be absorbed or released, but temperature remains constant.
Melting and Evaporating Phase Changes States of matter Energy Imfs Endo or Exo? H Sign Condensation and Solidification Phase Changes
Let s review Kinetic Energy Energy of motion, directly relates to the temperature of the substance Potential energy stored energy, the energy stored in the bonds
During a phase change Temperature stays the same Because kinetic energy stays the same As potential energy increases or decreases depending on the phase change Solid liquid or liquid gas: PE increases Gas liquid or liquid solid: PE decreases
Heating Curve
Definition Sign and energy movement ΔH fus - H fus ΔH vap -ΔH vap * Table 16-6 on page 502 in blue book for standard enthalpies of vaporization and fusion *
Definition Sign and energy movement ΔH fus Heat required to melt one mole of a solid Positive since E is absorbed and PE increases - H fus ΔH vap -ΔH vap * Table 16-6 on page 502 in blue book for standard enthalpies of vaporization and fusion *
Definition Sign and energy movement ΔH fus Heat required to melt one mole of a solid Positive since E is absorbed and PE increases - H fus Heat released to solidify one mole of a liquid Negative since E is released and PE decreases ΔH vap -ΔH vap * Table 16-6 on page 502 in blue book for standard enthalpies of vaporization and fusion *
Definition Sign and energy movement ΔH fus Heat required to melt one mole of a solid Positive since E is absorbed and PE increases - H fus Heat released to solidify one mole of a liquid Negative since E is released and PE decreases ΔH vap heat required to vaporize one mole of a liquid Positive since E is absorbed and PE increases -ΔH vap * Table 16-6 on page 502 in blue book for standard enthalpies of vaporization and fusion *
Definition Sign and energy movement ΔH fus Heat required to melt one mole of a solid Positive since E is absorbed and PE increases - H fus Heat released to solidify one mole of a liquid Negative since E is released and PE decreases ΔH vap heat required to vaporize one mole of a liquid Positive since E is absorbed and PE increases -ΔH vap heat released to condense one mole of a gas Negative since E is released and PE decreases * Table 16-6 on page 502 in blue book for standard enthalpies of vaporization and fusion *
Summary Solid H fusion Liquid H vaporization Gas Solid - H fusion Liquid - H vaporization Gas
Phase Change Problems Q = mδh Depending on the phase change you will either use ΔH vap or ΔH fus
Practice Problem How much heat is required to melt 233 grams of ice?
Warm up 1) How much heat is required to freeze 12.3 grams of water? 2) Convert 12,000 joules into kcal 1) Is it endo or exothermic a) Melting b) 2LiCl 2Li + Cl2 + 200 kj
Specific Heat amount of heat required to raise the temperature of one gram of a substance by one degree Celsius Units : J/g C You can specific heat values in the reference table
Think about it Which has a higher specific heat? Oven mitts or a piece of metal? Water or rocks?
Specific Heat-the formula! q= mcδt Specific Heat J/g C Amount of Heat (J) Mass (g) Change in Temperature (K or C)
Specific Heat Substance Specific Heat (J/g C) Water 4.184 Ice 2.03 Steam 2.01 Al (s) 0.897 Granite (s) 0.803 Iron (s) 0.449
Practice Problem 1 How much heat is lost when 4110 g of aluminum cools from 660 C to 25.0 C? The specific heat of aluminum is 0.903 J/g C
Warm Up: Reminder QUIZ TOMORROW! Lab due tomorrow! 1)How much heat is lost when a 2.5 gram sample of iron cools from 98 C to 45 C? 2) How much energy is needed to melt 16 grams of ice? 3) What is the empirical formula for N2H6? 4) Write the thermochemical equation for this reaction. (this means write the reaction with the enthalpy written as either a reactant or product) 2NH3 N2 + 3H2 ΔH = -125 Joules
Calorimeter Insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process q lost =-q gaine d mc T lost = -mc T gained
One kind of calorimeter works like this: A known amount of or reactants are sealed in a reaction chamber. The reaction chamber is immersed in a known quantity of water The water and reaction chamber are in an insulated vessel The energy given off (or absorbed) during the reaction is transferred to the water If the reaction released energy the water temperature increases If the reaction needs energy the water temperature decreases. Heat is not measured directly. Temperature is measured. Temperature is affected by the transfer of heat (energy).
Example A 20.0 g piece of metal at a temperature of 90.0 C is dropped into an insulated container holding 125 g of water at 20.0 C. If the final temperature is 23.0 C, what is the specific heat of the metal?
Heat of formation (ΔH f ) the heat absorbed or released when one mole of a compound is formed by a combination of its elemental parts this small circle indicates standard state: 1 atm and 25 C These values are found on page 902 in red textbook. Appendix A, Table A-14 The heat of formation of an element or diatomic molecule is ZERO kj/mole.
Heat of Formation H rxn n( H f of products) n( H f of reactants)
Try it! Calculate the H rxn and indicate if the reaction is endothermic or exothermic. 16H 2 S(g) + 8 SO 2 (g) 16 H 2 O(l) + 3 S 8 (s)
Heat of formation continued The heat of formation also indicates of the stability of a substance. These values are constant for compounds. Most stable? Least stable? Substance ΔH f Al 2 O 3(s) -1676 kj/mol NO (g) 90.29 kj/mol 142.7 kj/mol O 3(g)
Hess s Law The overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process.
Key ideas The major utility of Hess s Law is in calculating the enthalpy changes of reactions that would be difficult to measure. Note: according to the law of conservation of energy, energy cane neither be created nor destroyed in an ordinary chemical reaction. Hess s law tells us that we will never get more energy (or less energy for that matter) from a chemical reaction.
Example
Entropy Entropy (S) is the measure of disorder or randomness of the particles that make up a system. The Law of Disorder states that spontaneous processes always proceed in such a way that the entropy of the universe increases. (The second law of Thermodynamics)
Entropy From each group, select the part with the highest entropy: a. Increasing temperature or decreasing temperature of a substance b. Reactants or products: 2NH 3(g) 3H 2(g) + N 2(g) c. ice or water or steam
Entropy H2O(l) H2O(g) S system = + CH3OH(s) CH3OH(l) S system = + CO2(g) CO2(aq) S system = - 2SO 3 (g) 2SO 2 (g) + O 2 (g) S system > 0
Entropy 4.You can predict the change in entropy when a solid or a liquid dissolved to form a solution. NaCl(s) + H2O(l) NaCl(aq) S system > 0 (picture below) 5. An increase in temperature of a substance is always accompanied by an increase in the random motion of its particles. Entropy is positive.
Entropy Practice Predict the sign of S system for each of the following changes. CIF(g) + F 2 (g) CIF 3 (g) NH 3 (g) NH 3 (aq) CH 3 OH(l) CH 3 OH(aq) C 10 H 8 (l) C 10 H 8 (s)
Exothermic In an exothermic reaction, molecules collide with enough energy to overcome the activation energy (Ea), energy barrier, form an activated complex, then release energy and form products at a lower energy level.
Exothermic Change in Enthalpy is less than ZERO. For example: 4Fe + 3O 2 2Fe 2 O 3 H = -1625kJ
Endothermic In an endothermic reaction, the reactant molecules lying at a low energy level must absorb energy to overcome the activation energy barrier and form highenergy products.
Endothermic Change in Enthalpy is greater than ZERO. For example: NH 4 + NO 3 - NH 4 NO 3 H = +27 kj
Collision Theory 1. Reacting substances (atoms/ions/molecules) must collide. 2. Reacting substances must collide with sufficient energy to form activated complex. (Activation Energy = Ea)
Collision theory 3. Reacting substance must collide with the correct orientation.
Collision Theory
Collision Theory
Factors that affect reaction rates Nature of reactants More reactive the substance, the faster the reaction Concentration When increased, the rate increases (more collisions) Surface area More surface area quicker reaction Temperature Usually increasing temperature increases rate Catalysts Reaction takes a different path and lowers activation energy
Warm Up 1) How much heat is absorbed when 6.5 grams of water undergoes boiling? 2) What is the mass of a sample of iron that releases 1200 joules of heat when it is cooled from 90.0 C to 75.0 C? 3) What is the freezing point of the substance in the graph below?
Potential Energy Diagram
Catalyst A substance that increases the rate of a chemical reaction without itself being consumed in the reaction. An example of a catalyst is an enzyme
Equilibrium Reversible Reaction is one that can occur in both forward and reverse directions. Chemical equilibrium is a state in which the forward and reverse reactions balance each other because they take place at equal rates. Rate forward reaction = Rate reverse reaction
equilibrium Equilibrium is DYNAMIC, meaning that Equilibrium is a state of action. The reaction is constantly shifting and moving to maintain equilibrium even though we can not observe this.
Equilibrium Law of chemical equilbrium states that at a given temperature, a chemical system may reach a state in which a particular ratio of reactant to product concentrations has a constant value. aa + bb cc + dd Where A and B are the reactants, C and D are the products, and a, b, c, and d are the coefficients in a balanced equation.
Equilibrium Equilibrium constant (Keq) is the numerical value of the ratio of products concentrations to reactant concentrations, with each concentration raised to the power of its coefficients in the balanced equation. Keq= [C] c [D] d [A] a [B] b only liquids and aqueous substances can be put into the equilibrium constant
Equilibrium Keq > 1 : More products than reactants at equilibrium. Keq < 1 : More reactants than products at equilibrium.
Equilibrium Find the Equilibrium Expression for the following: 1. N 2 O 4 (g) 2NO 2 (g) 2. CO(g) + 3H 2 (g) CH 4 (g) + H 2 O(g) 3. 2H 2 S(g) 2H 2 (g) + S 2 (g)
Equilibrium Write the expression for the following: 1. C 10 H 8 (s) C 10 H 8 (g) 2. CaCO 3 (s) CaO(s) + CO 2 (g) 3. H 2 O(l) H 2 O(g) 4. FeO(s) + CO(g) Fe(s) + CO 2 (g)
Warm Up 1) Balance and classify the equation below KClO 3 (s) KCl (s) + O 2 (g) 2) Is this reaction endothermic or exothermic? 2NH 3 N2 + 3H 2 + 150 kj 3) Explain what each letter on the graph represents. Also label the activation complex
RUBRIC folded inside Reminder: test tomorrow! 1) how much energy is needed for 12 grams of water to undergo condensation? 2) What phase change occurs when solid calcium becomes a gas 3) Write the electron configuration for Lithium 4) What is the Keq expression for Na (s) + Cl 2 (g) 2 NaCl (s)
Le Chatelier
A stress can be: Change in concentration of product or reactant Change in temperature Change in pressure (just gases)
N 3H 2NH heat 2( g) 2( g) 3( g) This reaction is at equilibrium N 2 H 2 NH 3 heat What happens to the reaction if you increase the concentration of Nitrogen?
N 3H 2NH heat 2( g) 2( g) 3( g) Increase nitrogen concentration 1. How does the reaction need to shift to make it go back to equilibrium? Right 2. What will happen to all of the substances as a result?
N 3H 2NH heat 2( g) 2( g) 3( g) N 2 H 2 NH 3 heat How have things changed? N 2 H 2 NH 3 heat
https://www.youtube.com/watch?v=7zuuv455zfs
Changing Temperature This reaction is exothermic, meaning when you add heat you are adding to the product side of the reaction. K eq (equilbrium constant): is only affected by a temperature change When you increase the temperature the endothermic reaction is favored When you decrease the temperature the exothermic reaction is favored
N 2 H 2 NH 3 heat What happens when you increase the temperature? 1. How does the reaction need to shift to make it go back to equilibrium? Left 2. What will happen to all of the substances as a result?
N 3H 2NH heat 2( g) 2( g) 3( g) N 2 H 2 NH 3 heat How have things changed? N 2 H 2 heat NH 3
Changing Pressure Only affects equilibrium reactions with gaseous substances Think of your reaction in a closed container. When you increase pressure (decrease volume) you want to have less gas in your system When you decrease pressure (increase volume) you want to produce more gas in your system
Changing Pressure Rule Thumb When you INCREASE pressure: always shift toward fewer moles of gas! When you DECREASE pressure: always shift toward more moles of gas!
N 3H 2NH heat 2( g) 2( g) 3( g) Decrease Pressure Normal Increase Pressure
Try It! Ex 1: CH 4 (g) + 2H 2 S(g) CS 2 (g) + 4H 2 (g) a) Increase the pressure b) Decrease the pressure Ex 2: 2SO 3 (g) 2SO 2 (g) + O 2 (g) a) Increase the pressure b) Decrease the pressure