Name: _____________________________
1st & 2nd 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)
5) Determine ∆Sosys 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.