Chemistry 2 Exam 3 Professor Daniel Fried Na the change in free energy for the c

Question

Chemistry 2 Exam 3 Professor Daniel Fried Na the change in free energy for the combustion of methane at 30oK. Pay special attention to using comect units combustion of -890.3 k 242.8 J Answer 2. the reaction above was camed out at a very very high temperature, which A. The change in free energy would become negative. B. The change enthalpy would become positive. C. The change free energy would become positive D. The reaction would become spontaneous Find the change in entropy of the surroundings for the boiling of a mole of water at 400 K % 40.65 kJ/mole Answer 4 For a certain chemical reaction, the change in entropy of the system is +50 Jimol-K, and the change in entropy of the s is -1000 Jmol-K.Which is true? A. The change in Gibbs energy is-950 J/mol K. B. The change in Gibbs energy is -1050 J/mol-K. C. The change in entropy of the universe is -950 Jimol K D. The change in entropy of the universe is-1050 J/mol-K 5. Consider the reaction below. According to the common ion effect, what is the concentration of Pb2* when 1M NaCI is add The Kap of lead(ll) chioride is 1.7 X 10 s M Answer

Explanation / Answer

1)

CH4(g) + 2 O2(g) -------> CO2(g) + 2 H2O(l)

For the above reaction dH = -890 kJ/mol and dS = -242.8 J/mol K

dG = dH - T*dS

dG = -890 * 10^3 - (300*(-242.8))

dG = -817.16 kJ

2)

If we increase temperature then the dS value decreases since dS = Q/T,

so the entropy of products will be more so the reaction may become spontaneous reaction.

3)

dS = q/T

ds = dH0/T = 40.65 * 10^3/400

dS = 101.625 J/mol K

4)

we have,

dS total = dS system + dS surro

dS total = 50 -1000

dS total = -950 J/mol K is the entropy of the universe

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