Entropy and Enthalpy Guided Notes. a) Entropy. b) Enthalpy. c ) Spontaneous. d) Non-spontaneous

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1 Entropy and Enthalpy Guided Notes 1) Define a) Entropy b) Enthalpy c ) Spontaneous d) Non-spontaneous 2) There is a natural tendency for reaction to move to the side with enthalpy Minimum enthalpy is the side the heat term On a PE diagram, the tendency of minimum enthalpy favours the side that is Higher or lower on the graph. In an endothermic reaction ( forward), min. enthalpy favours the. In an exothermic reaction ( forward), min. enthalpy favours the. Problems Tell whether each of the following is endothermic or exothermic and state which has minimum enthalpy, the reactants or the products: a. PCl 5(g) Cl 2(g) + PCl 3(g) ΔH = 92.5 kj b 2NH 3(g) kj N 2(g) + 3H 2(g) c CO (g) + 3H 2(g) CH 4(g) + H 2 O (g) kj d. Cl 2(g) Cl 2(aq) ΔH = -25 kj

2 3) There is a natural tendency for reaction to move to the side with entropy There is a natural tendency towards the side of the reaction with more or less order List the phases by increasing entropy ( lowest to highest) The side of the reaction with more or less moles of gas has maximum entropy In the following examples, the entropy is increasing (or the products have greater entropy): 1. There is a gas (or gases) on the right, when there are no gases on the left of the equation: CaCO 3(s) + 2 HCl (aq) CaCl 2(aq) + CO 2(g) + H 2 O (l) a gas is formed on the right. 2. When there are gases on both sides, the products have greater entropy when there are more moles of gas on the right (add up coefficients of gases on left and right.): 4NH 3(g) + 5O 2(g) 4NO (g) + 6H 2 O (g) There are (4 + 5) = 9 moles of gas on the left There are (4 + 6) = 10 moles of gas on the right. Problems For each of the following, decide whether the reactants or the products have greater entropy: a) I 2(s) I 2(aq) The have greater entropy. b) 2NH 3(g) N 2(g) + 3H 2(g) The have greater entropy. c) NH 3(g) NH 3(aq) The have greater entropy. d) CO (g) + Cl 2(g) COCl 2(g) The have greater entropy.

3 e) MgCO 3(s) + 2HCl (aq) MgCl 2(aq) + H 2 O (l) + CO 2(g) The have greater entropy. 4) In nature there is a natural tendency for a reaction to favour the side with enthalpy and entropy. 5) Choose one of the following does not occur-non-spontaneous or goes to completion- spontaneous or goes to equilibrium a) If min. enthalpy and maximum entropy both favour the products - the forward reaction will -the reverse reaction will b) If min. enthalpy and maximum entropy both favour the reactants - the forward reaction will -the reverse reaction will c) If min. enthalpy and maximum entropy both favour the opposite directions - the forward reaction will -the reverse reaction will Problems 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. a) PCl 3(g) + Cl 2(g) PCl 5(g) ; ΔH = kj If PCl 3 and Cl 2 are put together, what should happen?(go to completion/ reach a state of

4 b) 2NO 2(g) N 2 O 4(g) + energy If NO 2 was put in a flask, what should happen?(go to completion/ reach a state of c) P 4 (s) + 6H 2(g) + 37 kj 4PH 3(g) If P 4(s) and 6H 2(g) was put in a flask, what should happen?(go to completion/ reach a state of d) 2PbO (s) + 4NO 2(g) + O 2(g) 2Pb(NO 3 ) 2(s) ; ΔH = kj The has/have maximum entropy. If PbO (s) and NO 2(g) were put in a flask, what should happen?(go to completion/ reach a state of

5 Self Test 1. What is meant by enthalpy? 2. What is meant by entropy? 3. In an endothermic reaction, the have minimum enthalpy. 4. In an exothermic reaction, the have minimum enthalpy. 5. Arrange the following in order from least entropy to greatest entropy: a) liquids b) gases c) aqueous solutions d) solids < < < 6. There is a natural tendency toward enthalpy and entropy. 7. A process in which entropy increases and enthalpy decreases will (go to completion/ reach a state of 8. A process in which entropy increases and enthalpy increases will (go to completion/ reach a state of 9. A process in which entropy decreases and enthalpy decreases will (go to completion/ reach a state of 10. A process in which entropy decreases and enthalpy increases will (go to completion/ reach a state of 11. A process in which both the enthalpy and entropy trends favour reactants will (go to completion/ reach a state of 12. A process in which both the enthalpy and entropy trends favour products will (go to completion/ reach a state of 13. A process in which the enthalpy and entropy trends oppose each other will (go to completion/ reach a state of

6 14. In each of the following, state which has the maximum entropy, (reactants or products) a) C (s) + O 2(g) CO 2(g) b) 2Al(s) + 6HCl (aq) 3H 2(g) + 2AlCl 3(aq) c) 2SO 3(g) 2SO 2(g) + O 2(g) d) HCl (g) H + (aq) + Cl - (aq) e) KOH (s) K + (aq) + OH - (aq) 15. 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. Assume there is sufficient activation energy to initiate any spontaneous reaction. a) PCl 5(g) PCl 3(g) + Cl 2(g) ; ΔH = kj The has/havemaximum entropy. If PCl 5 is put in a flask what should happen?(go to completion/ reach a state of b) 2NO (g) + O 2(g) 2NO 2(g) + energy If NO and O 2 were put in a flask, what should happen?(go to completion/ reach a state of c) Na 2 CO 3(s) + 2HCl (aq) 2NaCl (aq) + CO 2(g) + H 2 O (l) kj completion/ If Na 2 CO 3(s) + 2HCl (aq) were put in a flask, what should happen?(go to reach a state of

7 d) 2Pb(NO 3 ) 2(s) kj 2PbO (s) + 4NO 2(g) + O 2(g) ; If Pb(NO 3 ) 2 was put in a flask, what should happen?(go to completion/ reach a state of 16. Reactions which result in a/an in enthalpy and a/an in entropy will always be spontaneous. 17. Reactions which result in a/an in enthalpy and a/an in entropy will always be non-spontaneous.