Download 1 - UCSB C.L.A.S.

1. Define the following:
a. energy
b. kinetic energy
c. potential energy
d. first law of thermodynamics
e. work
f. heat
g. system vs surroundings
h. open system, closed system and isolated system
i. enthalpy
j. Cv
k. Cp
2. Predict whether q, w, and ΔE are positive, negative or zero for:
a. heating 2 moles of nitrogen gas in a rigid container from 100 K to 200 K
b. cooling 1 mole of helium gas from 50 °C to 25 °C at a constant pressure of 1 atm.
c. expanding 1 mole of argon gas from 1 L to 2 L at constant temperature
d. melting 1 mole of ice at 0 °C and constant pressure of 1 atm
e. boiling (evaporating) 1 mole of liquid water at 100 °C and constant pressure of 1 atm
f. burning 1 mole of propane gas at constant pressure of 1 atm
C3H8 (g) + 5 O2 (g) →
3 CO2 (g) + 4 H2O (g)
3. Calculate the value of ΔE, ΔH, q and w for the following:
a. heating 500. g of nitrogen gas from 50.0 ºC to 75.0 ºC at constant volume (Cv = 20.71 J/K
mol, Cp = 29.03 J/K mol)
b. cooling 500. g of nitrogen gas from 75.0 ºC to 50.0 ºC at a constant pressure of 1 atm
4. For a specific gas, why is the value of Cp always greater than Cv? By what value are they
always related?
1. Assume you have 2 mol of argon gas at a pressure of 10 atm and volume 1.0 L and the gas is
taken to a new state where the pressure is 5 atm and the volume is 5 L. There are two possible
paths for this process. Use the following diagram to calculate ΔE, ΔH, q and w for each
pathway.
2. How many joules are required to raise the temperature of 225 g of copper from 25.0 to 35.0
ºC? (c = 0.20 J/ºC g)
3. If a 50.0 g sample of copper is heated to 85.0 ºC and placed in 100 mL water initially at 25.0
ºC, what will be the final temperature of the solution assuming no heat is lost to the
surroundings? (cwater = 4.18 J/ºC g)
4. Consider the reaction:
CaCl2(s) → Ca2+(aq) + 2Cl-(aq)
ΔH = -81.5 kJ
If 20.0 g of calcium chloride are dissolved in 150 mL of water at 25.0 C, what will be the final
temperature of the solution assuming no heat loss to the surroundings?
5. Define the following and draw energy diagrams to represent the relative position of reactants
and products.
a. exothermic reaction
b. endothermic reaction
6. Consider the following reactions. Predict the sign on work for each (is work done on the
system, by the system or neither?) State whether ∆E is greater than, less than or equal to ∆H.
a. H2O(l) → H2O (g)
b. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
c. N2(g) + 3H2(g) → 2NH3(g)
7. Define the term Standard enthalpy of formation ( ΔHf º):
Also write the reaction that corresponds to the enthalpy of formation for the following:
a. CH4(g)
b. NaCl(s)
c. C6H12O6(s)
8. How much heat is released when methane (CH4) is burned? Use the following:
ΔHfº
CH4(g)
-75 kJ/mol
CO2(g)
-393.5 kJ/mol
H2O(g)
-242 kJ/mol
(hint: write the combustion reaction and find ΔH)
9. Use Hess’s Law to calculate ΔH for the reaction:
P4O10(s) + 6PCl5(g) → 10Cl3PO(g)
Given the following:
P4(s) + 6Cl2(g) → 4PCl3(g)
ΔH = -1225.6 kJ
P4(s) + 5O2(g) → P4O10(s)
ΔH = -2967.3 kJ
PCl3(g) + Cl2(g) → PCl5(g)
ΔH = -84.2 kJ
PCl3(g) + ½ O2(g) → Cl3PO(g)
ΔH = -285.7 kJ
Ideal Gases
Constant P
Chemical Rxns
Constant T
Constant V
q
w
∆E
∆H
1. Calculate q,w, ∆E and ∆H for the following:
a. heating 1.00 kg of ethane gas (C2H6) from 25.0 to 75.0 °C at a constant pressure of 2.00 atm
(Cv and Cp are 44.60 and 52.92 J/K mol respectively)
b. cooling 1.00 kg of ethane gas from 75.0 to 25.0 °C at constant volume
c. burning 1 mole of propane gas to give carbon dioxide and liquid water at constant pressure of
1.00 atm and a temperature of 25 °C
( ∆Hcombustion = -2222 kJ)
2. If 450. J are required to raise the temperature of 225 g of copper from 25.0 to 35.0 ºC, what is
the heat capacity of copper?
3. If a 50.0 g sample of copper is heated to 85.0 ºC and placed in 100 mL water initially at 25.0
ºC, what will be the final temperature of the solution assuming no heat is lost to the
surroundings? (cwater = 4.18 J/ºC g)
4. Consider the reaction:
CaCl2(s) → Ca2+(aq) + 2Cl-(aq)
ΔH = -81.5 kJ
If 20.0 g of calcium chloride are dissolved in 150 mL of water at 25.0 C, what will be the final
temperature of the solution assuming no heat loss to the surroundings?
1. What is Hess’ Law?
2. Use Hess’ Law to find ∆H for the reaction:
2C (s) + O2 (g) → 2 CO (g)
Given the following
CO2 (g) → C (s) + O2 (g)
∆H = 394 kJ
CO2 (g) → CO (g) + ½ O2 (g)
∆H = 283 kJ
3. Use Hess’s Law to calculate ΔH for the reaction:
P4O10(s) + 6PCl5(g) → 10Cl3PO(g)
Given the following:
P4(s) + 6Cl2(g) → 4PCl3(g)
ΔH = -1225.6 kJ
P4(s) + 5O2(g) → P4O10(s)
ΔH = -2967.3 kJ
PCl3(g) + Cl2(g) → PCl5(g)
ΔH = -84.2 kJ
PCl3(g) + ½ O2(g) → Cl3PO(g)
ΔH = -285.7 kJ
4. Define the term Standard enthalpy of formation ( ΔHf º):
Also write the reaction that corresponds to the enthalpy of formation for the following:
a. CH4(g)
b. NaCl(s)
c. C6H12O6(s)
5. Use the data below to calculate ∆H for the following reactions:
CO2 (g)
H2O (g)
NH3 (g)
∆Hf °
-394
-242
-46
a. N2 (g) + 3 H2 (g)
→
2 NH3 (g)
b. 4 NH3 (g)
+ 7 O2 (g)
→
4 NO2 (g)
+
NO2 (g)
34
kJ/mol
6 H2O (g)
6. If the combustion reaction of methane has a ∆H value of -803 kJ/mol, find the standard
enthalpy of formation of methane. (hint: write the reaction and use the data above)