1St Law of Thermodynamics Worksheet

Name: ______

1 st & 2 nd laws of Thermodynamics Worksheet

*Use significant figures and show your work.

1) Two gases, A and B are confined in a cylinder-and-piston arrangement. Substances A and B react to form a solid product, C. As the reaction occurs, the system loses 1150 J of heat to the surroundings. The piston moves downward as the gases react to form a solid. As the volume of the gas decreases under the constant pressure of the atmosphere, the surroundings do 480 J of work on the system. What is the change in the internal energy of the system in J?

2) A gas is compressed in a cylinder by a constant pressure of 10. atm from a volume of 20.0 L to 2.00 L. Calculate the work (in J) done on the system.

3) A gas is allowed to expand at constant temperature from a volume of 1.00 L to 10.1 L against an external pressure of 0.50 atm. If the gas absorbs 250 J of heat from the surroundings, what are the values of q, w and ∆E?

4) Describe the ∆S values for the following reactions.

1. CH4 (g) + H2O (g)  CO (g) + 3H2 (g)

2. C (s) + O2 (g)  CO2 (g)

3. H2O2 (l)  H2O (l) + ½ O2 (g)

o 5) Determine ∆S sys for the following reaction in J/K:

SO3 (g) + H2O (l)  H2SO4 (l) 6) For a certain chemical reaction, ∆Ho = -19.5 kJ and ∆So = + 42.7 J/K. a. Is the reaction exothermic or endothermic?

b. Does the reaction lead to an increase or decrease in the disorder of the system?

c. Is the reaction spontaneous at 298 K under standard conditions?

7) Calculate the standard free-energy changes for the following reactions at 25.0°C.

a. H2(g) + Br2(l)  2HBr(g)

b. 2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(l)

8) Find the temperature (in K) at which reactions with the following ΔH and ΔS values would become spontaneous. a. ΔH = -126 kJ ΔS = 84 J/K

b. ΔH = -11.7 kJ ΔS = -105 J/K

9) Consider the following reaction

4Fe(s) + 3O2(g)  2Fe2O3 (s)

By determining the sign of ΔSuniv mathematically, show if this rxn is spontaneous under standard state conditions at 25.0°C.