Equil Entropy Enthalpy Worksheet answers

Chemistry 12 Unit 2 - Chemical Equilibrium Worksheet 2-1 - Equilibrium, Enthalpy and Entropy 1. What do people mean when they say that a reaction is reversible? Having Forward and reverse rxns 2. Give four things which are true about a system at equilibrium: 1. closed system achieved from either direction 2. constant temperature [products]   = constant = [reactants] 3. forward rate = reverse rate 4. constant macroscopic properties or we can measure 3. What is meant by macroscopic properties? properties we can see 4. Give some examples of macroscopic properties: colour, gas produced, mass change 5. What happens to macroscopic properties at equilibrium? constant 6. How do the rates of the forward and reverse reaction compare at equilibrium? equal 7. Do the forward and reverse reactions stop at equilibrium? no 8. What can be said about the concentrations of all reactants and products at equilibrium? constant 9. Why is chemical equilibrium called dynamic equilibrium? molecular changes take place   Worksheet 2-1 - Equilibrium, Enthalpy and Entropy Page 1 Chemistry 12 Worksheet 2-1-Equilibrium, Enthalpy and Entropy Page 2 A+BC+D 1000 Keq = (0.8)2 / (0.2)2 = 16 0.2 0.2 0.8 0.8 10. Given the reaction: A + B ⇌ C + D When 1.0 mole of A is combined with 1.0 mole of B, an equilibrium is established in which [A] = 0.2 M, [B] = 0.2 M, [C] = 0.8 M and [D] = 0.8 M. If, at the same temperature, 1.0 mole of C and 1.0   mole of D are combined. When equilibrium is established, determine what the following concentrations will be: [A] = 0.2 M, [B] = 0.2 M, [C] = 0.8 M and [D] = 0.8 M 11. Given sufficient activation energy, a system not at equilibrium will eventually move toward equilibrium. 12. Systems will tend toward a position of minimum enthalpy. ΔH 13. Systems will tend toward a position of maximum entropy. ΔS 14. Tell whether each of the following is endothermic or exothermic and state which has minimum enthalpy, the reactants or the products: a. Cl2(g) + PCl3(g)   ⇌ PCl5(g) ΔH = -92.5 kJ exothermic and the product has minimum enthalpy. b. 2NH3(g) ⇌ N2(g) + 3H2(g) ΔH = 92.4 kJ endothermic and the reactant has minimum enthalpy. c. CH4(g) + H2O(g) + 49.3 kJ ⇌ CO(g) + 3H2(g) endothermic and the reactants have minimum enthalpy. 15. If the reaction: Cl2(g) ⇌ Cl2(g) ΔH = +25 kJ was proceeding to the right, the enthalpy would be increasing. Is this a favourable change? No 16. If the reaction: N2(g) + 3H2(g) ⇌ 2NH3(g) + 92.4 kJ was proceeding to the right, the enthalpy would be decreasing. Is this a favourable change? Yes Chemistry 12 Unit 2 - Chemical Equilibrium Worksheet 2-1 - Equilibrium, Enthalpy and Entropy 17. For each of the following, decide whether the reactants or the products have greater entropy: a) I2(s) ⇌ I2(g) The product has greater entropy. b) 4PH3(g) ⇌ P4(g) + 6H2(g) The products have greater entropy. c) NH3(g) ⇌ NH3(aq) The reactant has greater entropy. 18. When the two tendencies oppose each other (one favours reactants, the other favours products), the reaction will   reach equilibrium. Processes in which both the tendency toward minimum enthalpy and toward maximum entropy favour the products, will go to completion   (100% product formation). Processes in which both the tendency toward minimum enthalpy and toward maximum entropy favour the reactants, will not take place (no   rxn). 19. For each of the following reactions decide which has minimum enthalpy (reactants or products), which has maximum entropy (reactants or products), and if the reactants are mixed, what will happen? (go to completion/reach a state of equilibrium/not occur at all). a) 4HCl(g) + O2(g)   ⇌ 2H2O(g) + 2Cl2(g) ΔH = -114.4 kJ The reactants have minimum enthalpy. The products have maximum entropy. If HCl + O2 are put together, what should happen? (go to completion/reach a state of equilibrium/not occur at all) b) CO2(g) + H2(g)   ⇌ CO(g) + H2O(g); ΔH = 42.6 kJ The reactants have minimum enthalpy. How does the entropy of the reactants and products compare? no change If CO2(g) + H2(g) were put in a flask, what should happen? (go to completion/reach a state of equilibrium/not occur at all) not occur at all   Worksheet 2-1 - Equilibrium, Enthalpy and Entropy Page 3 Chemistry 12 Unit 2 - Chemical Equilibrium Worksheet 2-1 - Equilibrium, Enthalpy and Entropy c) 4PH3(g) ⇌ P4(g) + 6H2(g) + 37 kJ The products have minimum enthalpy. The products have maximum entropy. If PH3(g) was put in a flask, what should happen? (go to completion/reach a state of equilibrium/not occur at all) go to completion 20. Do systems always reach minimum enthalpy at equilibrium? No Explain.   ΔS, ΔH Entropy may be higher than enthalpy 21. Do systems always reach maximum entropy at equilibrium? No Explain. ΔH, ΔS Enthalpy may be higher than entropy 22. A "heat term" in a chemical equation shows what is happening to the enthalpy and really has nothing to do with the entropy (Answers are either entropy or enthalpy) 23. As a reaction approaches equilibrium, the rate of the forward reaction decreases. Once equilibrium is reached, the rates become equal. While the rate of the reverse reaction increases 24. Consider the reaction: BaCO3(s) + heat ⇌ BaO(s) + CO2(g) Which one of the following observations will indicate that the reaction has most likely achieved equilibrium? a) The mass of the system becomes constant b) The concentration of   BaO(s) becomes constant c) All the BaCO3 is consumed. d) The gas pressure of the system becomes constant Your answer is (d) The gas pressure of the system becomes constant Explain why. solids don't affect the equilibrium 25. Consider the following reaction: Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq) A solution of Fe(NO3)3 is added to a solution of KSCN. As equilibrium is being established, the [Fe3+] is decreased and the [FeSCN2+] is increased. Worksheet 2-1 - Equilibrium, Enthalpy and Entropy Page 4