Ch. 19 AP Practice Calculations Name __________________

Date ______________

Period ____________

1. Given the following data for graphite and diamond at 298 K,

S^o(diamond) = 0.58 cal/mole

S^o (graphite) = 1.37 cal/mole

H^o_f CO₂ (graphite) = - 94.48 kilocalories/mol

H^o_f CO₂ (diamond) = - 94.03 kilocalories/mol

Consider the change: C(graphite) = C(diamond) at 298 K and 1 atmosphere.

a. What are the values of ∆S^o and ∆H^o for the conversion of graphite to diamond.

b. Perform a calculation to show whether it is thermodynamically feasible to produce diamond from graphite at 298 K and 1 atmosphere.

2. a. State the physical significance of entropy.

b. From each of the following pairs of substances, choose the one expected to have the greater absolute entropy. Explain your choice in each case. Assume 1 mole of each substance.

1. He(g) at 1 atmosphere and He(g) at 0.05 atmosphere, both at the same temperature.

2. H₂O(l) or CH₃CH₂OH(l) at the same temperature and pressure.

3. Mg(s) at 0^oC or Mg(s) at 150^oC, both at the same pressure.

E.C. Pb(s) or C(graphite) at the same temperature and pressure. (hint: compare bonding types)

3. PCl₅(g) à PCl₃(g) + Cl₂(g)

For the reaction above, ∆H^o = +22.1 kilocalories per mole at 25^oC

1. Does the tendency of reactions to proceed to a state of minimum energy favor the formation of the products of this reaction? Explain.
2. Does the tendency of reactions to proceed to a state of minimum entropy favor the formation of the products of this reaction? Explain.
3. State whether an increase in temperature drives this reaction to the right(favor the products), to the left(favor the reactants), or has no effect. Explain.
4. State whether a decrease in the volume of the system at constant temperature drives this reaction to the right, left, or has no effect. Explain.

4.

Substance	Enthalpy of Combustion (kJ/mol)	Absolute Entropy (J/mol K)
C(s, graphite)	- 393.5	5.740
H2(g)	- 285.8	130.6
C2H5OH(l)	- 1366.7	160.7
H2O(l)	-	69.91

a. Write a separate, balanced chemical equation for the combustion of each of the following: C(s), H₂(g), and C₂H₅OH(l). Consider the only products to be CO₂ and/or H₂O(l)

b. In principle, ethanol can be prepared by the following reaction:

2 C(s) + 2 H₂(g) + H₂O(l) à C₂H₅OH(l)

Calculate the standard enthalpy change for the preparation of ethanol,

as shown in the reaction above.

c. Calculate the standard entropy change for the reaction given in part b.

d. Calculate the value of the equilibrium constant at 25^oC for the reaction represented by the equation in part b.