BIOB111_CHBIO - Tutorial activities for Session 4

Transcription

1 BIOB111_CHBIO - Tutorial activities for Session 4 General topics for the week Discussion of the effect of several factors on chemical equilibrium of selected reactions. Examples of effect of stress on equilibrium reactions are given and students are asked to complete the work sheet on this topic. Chemical reactions and rates of chemical reactions Instructions: Use the following link to learn more about Le Châtelier s principle: < (link verified 13 January 2017) Use the following link to understand Chemical Equilibrium: (link verified 13 January 2017) General tutorial questions: 1. I) What is a reversible reaction? II) Use the information from the diagram below to describe what happens at a chemical equilibrium with respect to rates of the forward and backward reaction? II) Use the information from the following diagram to describe what happens at a chemical equilibrium with respect to the concentrations of the reactants and products? Last updated on 5-Feb-14 Page 1 of 10

2 2. Fill in the blanks with the given words: Choose from: the same time, does not change, quickly. A reversible reaction is when the forward reaction and reverse reaction occur at A reversible reaction uses up the reactants until a point (the equilibrium) where concentration of the reactants A reversible reaction rapidly produces a large and rapid increase in the concentration of products until a point (the equilibrium) where concentration of the products 3. Fill in the blanks with the given words: Choose from: the concentration of reactants, temperature, catalyst, exothermic, slower, faster. A chemical reaction in which a substance combines with oxygen releasing a large amount of energy as heat is a (n) reaction The rate of a chemical reaction can be increased by increasing of,, and adding a(n) Last updated on 5-Feb-14 Page 2 of 10

3 As reactants are used up and products accumulate the rate of forward reaction becomes Slower, while the rate of reverse reaction becomes 4. Identify each reaction as either endothermic or exothermic: Chemical Reaction Endothermic or Exothermic ΔH, change in heat energy C(s) + O 2 CO kcal (393 kj) ΔH = kcal (- 393 kj) 4Fe (s) + 3 O 2 (g) 2Fe 2O MJ (406.1kcal) ΔH = - 1.7MJ ( kcal) N 2(g) + O 2 (g) +21.6kcal 2NO (g) ΔH = 21.6 k cal 2H 2S (g) 2H 2 (g) + S 2 (s)+ Heat ΔH = negative (state if positive or negative) 5. Whether a reaction is exothermic or endothermic is determined by: a. The activation energy b. The physical state of the reactants c. How reactant and product potential energies compare d. Whether a catalyst is present 6. What happens when NH 3 is added to the chemical system (reaction) that is at equlibrium: N 2 + 3H 2 2NH 3 a. The rate of the forward reaction increases, as additional product is made b. The rate of the backward reaction increases, as additional product is made c. The rate of the backward reaction increases, as additional reactants are made d. The rate of the forward reaction increases, as additional reactants are made 7. What happens when N 2 is added to the chemical system (reaction) that is at equlibrium: N 2 + 3H 2 2NH 3 a. The rate of the forward reaction increases, as additional product is made b. The rate of the backward reaction increases, as additional product is made c. The rate of the backward reaction increases, as additional reactants are made d. The rate of the forward reaction increases, as additional reactants are made 8. What happens when H 2 is removed to the chemical system (reaction) that is at equlibrium: N 2 + 3H 2 2NH 3 Last updated on 5-Feb-14 Page 3 of 10

4 a. The rate of the forward reaction increases, as additional product is made b. The rate of the backward reaction increases, as additional product is made c. The rate of the backward reaction increases, as additional reactants are made d. The rate of the forward reaction increases, as additional reactants are made Last updated on 5-Feb-14 Page 4 of 10

5 Conceptual multiple choice questions: 1. Reactants are converted to products through chemical reactions. Chemical bonds are both formed and broken during a chemical reaction. Chemical reactions are also dependent on collisions between the components of the reaction. Which of the following accurately describes how a chemical reaction proceeds from the beginning to the end? a) After a collision between the reactant compounds some of the bonds within the reactants are broken, allowing atoms to be rearranged before new bonds are formed to generate the products b) In a chemical reaction bonds will form within the reactant compounds, before a collision between the product compounds, where some of the chemical bonds will be broken c) A collision between the reactant compounds begins the chemical reaction, where bonds are formed in the reactant compounds before they are converted into the product compounds, in which bonds are broken d) To begin the chemical reaction the chemical bonds that hold the reactant compounds together will break, which leads to a collision between the reactants, allowing new bonds to form which creates the product compounds 2. Chemical reactions rely on the collisions between the reactant compounds to begin the chemical reaction. Which of the following accurately describes the chemical reaction below? NO + O 3 NO 2 + O 2 a) Any collision between the reactants NO and O 3 will begin the chemical reaction, allowing some of the bonds within the reactants to be broken, so that new bonds can form to generate the products NO 2 and O 2 b) When the reactants NO and O 3 collide with sufficient force to meet the activation energy, new bonds are formed within the reactant compounds, which allows bonds to be broken in the products NO 2 and O 2 c) Any collision between the reactants NO and O 3 will begin the chemical reaction, allowing new bonds to form within the reactant compounds, which allows bonds to be broken in the products NO 2 and O 2 Last updated on 5-Feb-14 Page 5 of 10

6 d) When the reactants NO and O 3 collide with sufficient force to meet the activation energy, some of the bonds within the reactants will be broken, allowing new bonds to form which generate the products NO 2 and O 2 3. Rearrangement of the atoms is required to change the chemical structure of a compound. This occurs during a chemical reaction, where reactant compounds are converted into products, which is facilitated by the breakage and formation of chemical bonds. At what stage of a chemical reaction are chemical bonds broken and does this require or release energy? a) After collision between the products, bonds are broken within the product compounds which requires energy b) After collision between the reactants, bonds are broken within the reactant compounds which requires energy c) After collision between the products, bonds are broken within the product compounds which releases energy d) After collision between the reactants, bonds are broken within the reactant compounds which releases energy 4. Rearrangement of the atoms is required to change the chemical structure of a compound. This occurs during a chemical reaction, where reactant compounds are converted into products, which is facilitated by the breakage and formation of chemical bonds. At what stage of a chemical reaction are chemical bonds formed and does this require or release energy? a) New chemical bonds are formed, which releases energy, to create the products of a chemical reaction b) New chemical bonds are formed, which releases energy, to create the reactants of a chemical reaction c) New chemical bonds are formed, which requires energy, to create the products of a chemical reaction d) New chemical bonds are formed, which requires energy, to create the reactants of a chemical reaction Last updated on 5-Feb-14 Page 6 of 10

7 5. The energy barrier that must be overcome to begin a chemical reaction is called the activation energy. After a collision occurs between the reactant compounds, which exceeds the activation energy, the chemical reaction begins converting the reactants into the products. How does the amount of activation energy required for the chemical reaction impact on how often the reaction will occur (rate of the reaction)? a) Chemical reactions with low activation energies convert reactants into products occur more often than chemical reactions that have high activation energies b) Only chemical reactions with a high activation energies can occur often without a large energy input c) Chemical reactions with high activation energies convert reactants into products occur more often than chemical reactions that have low activation energies d) Different chemical reactions occur at the same rate irrespective of their activation energies 6. For an endothermic chemical reaction energy is absorbed (reactant) during the chemical reaction to convert the reactants into the products. In contrast, for an exothermic chemical reaction, energy is released as heat (product). Which of the following accurately describes the activation energy of an endothermic reaction & how often the reaction will occur? a) Endothermic reactions have high activation energies, meaning these chemical reactions do not occur often b) Endothermic reactions have low activation energies, meaning these chemical reactions occur often c) Endothermic reactions have high activation energies, meaning these chemical reactions occur often d) Endothermic reactions have low activation energies, meaning these chemical reactions do not occur often 7. For an endothermic chemical reaction energy is absorbed (reactant) during the chemical reaction to convert the reactants into the products. In contrast, for an exothermic chemical reaction, energy is released as heat (product). Which of the following accurately Last updated on 5-Feb-14 Page 7 of 10

8 describes the activation energy of an exothermic reaction & how often the reaction will occur? a) Exothermic reactions have low activation energies, meaning these chemical reactions do not occur often b) Exothermic reactions have high activation energies, meaning these chemical reactions occur often c) Exothermic reactions have high activation energies, meaning these chemical reactions do not occur very often d) Exothermic reactions have low activation energies, meaning these chemical reactions occur often 8. The rate of a chemical reaction can be sped up or slowed shown by adjusting the temperature or changing the concentration (amount) of the reactant and product compounds. How would you change the temperature to increase the rate of the chemical reaction and why? a) Decrease the temperature so that the reactant compounds are less likely to collide with each other to begin the reaction b) Increase the temperature so that the reactant compounds are more likely to collide with each other to begin the reaction c) Increase the temperature so that the reactant compounds are less likely to collide with each other to begin the reaction d) Decrease the temperature so that the reactant compounds are more likely to collide with each other to begin the reaction 9. The rate of a chemical reaction can be sped up or slowed shown by adjusting the temperature or changing the concentration (amount) of the reactant and product compounds. How would you change the concentration of the reactant compounds to increase the rate of the chemical reaction and why? a) Make the concentration of all of the different reactant compounds the same to increase the likelihood that they will collide to begin the reaction b) Decrease the concentration of all of the reactant compounds to to increase the likelihood that they will collide to begin the reaction Last updated on 5-Feb-14 Page 8 of 10

9 c) Double the concentration of all of the reactant compounds to increase the likelihood that they will collide to begin the reaction d) Increase the concentration of one of the reactant compounds, but decrease the concentration of the reactant compound, to increase the likelihood that they will collide to begin the reaction 10. Reversible chemical reactions can proceed in both the forward & reverse directions. What are the rates of the forward & reverse reactions in the reaction below when the reaction is at equilibrium? N 2 + 3H 2 2NH 3 a) Equilibrium reactions can only precede in a single direction b) The rate of the backward reaction exceeds the rate of the equilibrium reaction c) The rate of the forward reaction exceeds the rate of the backward reaction d) The rate of the forward reaction is equal to the rate of the backward reaction 11. Once a chemical reaction has reached equilibrium the equilibrium can be disrupted by stresses such as the addition/removal of components of the reaction or changes in temperature. What would happen to a chemical reaction once a stress pushes the reaction out of equilibrium? N 2 + 3H 2 2NH 3 a) The chemical reaction will remain in a non-equilibrium state b) The chemical reaction will increase the rate of either the forward or backward reaction in order to correct the stress so that the chemical reaction can return to equilibrium c) The chemical reaction can return to equilibrium without adjusting the rates of the forward or backward reaction d) The chemical reaction will remain in a non-equilibrium state until another stress Last updated on 5-Feb-14 Page 9 of 10

10 Last updated on 5-Feb-14 Page 10 of 10