chapter 5 thermochemistry

Question 1

If 10 J of heat is transferred to the surroundings from the system and the system does 20 J of work on the surroundings, what is the change in internal energy for the system?
a. -30 J
b. -10 J
c. 10 J
d. 30 J
e. 200 J

Answer 1

-30 J
The wording messed me up but, if you read it closely, the system is losing J in both instances.

Question 2

If 150 J of heat is transferred from the system to the surroundings and the system does 40 J of work on the surroundings, what is the change in internal energy of the system?
a. 150 J
b. 110 J
c. 190 J
d. -110 J
e. -190 J

Answer 2

-190 J

Question 3

If 320 J of heat is transferred from the surrounding to the system and the system does 110 J of work on the surroundings, what is the change in internal energy of the system?
a. -430 J
b. 210 J
c. 430 J
d. -320 J
e. -210 J

Answer 3

210 J

Question 4

A bomb calorimeter has a heat capacity of 210 J/C degrees
How much heat is required to raise its temperature 5 degrees C?
a. 42 J
b. 42 kJ
c. 1.05 kJ
d. 105 J
e. 215 J

Answer 4

1.05 kJ

Question 5

How much heat would be required to raise the temperature of 10 grams of water from 20 degrees C to 50 degrees C?
specific heat of water = 4.18 J / grams times degrees C
a. 1254 J
b. 2090 J
c. 125 J
d. 836 J
e. 12.5 kJ

Answer 5

1254 J
4.18 times 10 grams times 30 degrees

Question 6

How much heat would it take to melt 54 grams of ice at 0 degrees C
fusion for water = 6010 J / mole
a. 2000 J
b. 3000 J
c. 9000 J
d. 18,000 J
e. 24,000 J

Answer 6

18,000 J
First step; convert to moles

Question 7

The fusion for water is 6009 J / mole
How much heat would be required to melt 72 grams of ice at 0 degrees C?
a. 83 J
b. 6.0 kJ
c. 24 kJ
d. 83 kJ
e. 433 kJ

Answer 7

24 kJ

Question 8

How much heat is required to raise the temperature of 9 grams of ice at 0 degrees C to liquid water at 5 degrees C?
specific heat of water = 4.18 J / gram times degrees C
fusion = 6010 J / mole of water

Answer 8

3200 J
First you have to melt the ice. You will need 3,005 Jules to do this.
Plus, then you need to raise the temp 5 degrees C which will be 4.19 times 9 grams times 5 degrees.
Add them up to get approximately 3200 Jules
I actually got 3193

Question 9

A hot piece of iron is placed in 54 grams of H2O at 25 degrees C. After reaching thermal equilibrium, the temperature of the water is 35 degrees C. What is the change is heat (q) of the iron?
(specific heat of water 4.18 J/grams x degree C)
a. 1100 J
b. 0
c. -2260 J
d. -1100 J
e. 2260 J

Answer 9

-2260 J
specifically -2257.2
You really just calculate how much energy the iron gave the water and then realize that it lost that much energy making the answer a negative number.

4.18 x 54 x 10

Question 10

The following reaction occurs in the hydrogen fuel cell:
2H2 + O2 = 2H2O
change in heat = -484 kJ
How much heat is released during the consumption of 10 moles of H2?
a. 4840 kJ
b. 242 kJ
c. 48.4 kJ
d. 2420 kJ
e. 242 J

Answer 10

2420 kJ
The wording of the question leads the answer to not be negative.

Question 11

The enthalpy of combustion of acetylene is -1310 kJ
C2H2 + 5/2 O2 = 2CO2 + H2O
change in heat = -1310 kJ
How much heat is released from the combustion of 39 grams of acetylene (C2H2)?
a. 873 kJ
b. 1965 kJ
c. 34 kJ
d. 51,100 kJ
e. 1.2 kJ

Answer 11

1965 kJ

I don’t know why it gives you the change in heat twice in the question but it did so I’m copying it that way.

Question 12

Based on the provided data, what is the change in Heat for the following reaction?
C2H6 + 3Cl2 = 2CHCl3 + 2H2

C2H6 + H2 = 2CH4 change Heat +10 kJ
H2 + Cl2 = 2HCl change Heat -185 kJ
CH4 + 3Cl2 = CHCl3 + 3HCl change Heat -336 kJ

a. -511 kJ
b. 511 kJ
c. 1237 kJ
d. 127 kJ
e. -107 kJ

Answer 12

To make the provided reactions add up to the desired reaction the first reaction must be added as is to make the C2H6(g) appear as needed. The third reaction must be doubled to make the CHCl3(g) appear as needed. The second reaction must be reversed and tripled to cancel out the 6HCl(g) from the third reaction and to make both the H2(g) and Cl2(g) appear as needed.

C2H6(g) + H2(g) → 2CH4(g) ΔH˚ = +10kJ

2CH4(g) + 6Cl2(g) → 2CHCl3(g) + 6HCl(g) ΔH˚ = 2(-336kJ)

6HCl(g) → 3H2(g) + 3Cl2(g) ΔH˚ = (-3)(-185kJ)

C2H6(g) + H2(g) + 2CH4(g) + 36Cl2(g) + 6HCl(g) →

2CH4(g) + 2CHCl3(g) + 6HCl(g) + 23H2(g) + 3Cl2(g)

This reduces to the desired reaction:

C2H6(g) + 3Cl2(g) → 2CHCl3(g) + 2H2(g) ΔH˚ = 10 – 672 + 555

answer: ΔH˚ = -107kJ

Question 13

Based on the provided data, what is the change in Heat for the following reaction?
Cl2 + 2SO2 = SO3 + SOCl2

SO2 + 1/2 O2 = SO3 change Heat -98 kJ
SOCl2 + 1/2 O2 = SO2 + Cl2 change Heat -51 kJ

a. 149 kJ
b. -149 kJ
c. -47 kJ
d. 200 kJ
e. -200 kJ

Answer 13

To make the provided reactions add up to the desired reaction the second reaction must be reversed to make the Cl2(g) appear as needed, and the first reaction must be added as is to make the SO3(g) appear as needed.

SO2(g) + Cl2(g) → SOCl2(g) + ½O2(g) ΔH˚ = +51kJ

SO2(g) + ½O2(g) → SO3(g) ΔH˚ = -98kJ

SO2(g) + Cl2(g) + SO2(g) + ½O2(g) → SOCl2(g) + ½O2(g) + SO3(g)

This reduces to the desired reaction:

Cl2(g) + 2SO2(g) → SO3(g) + SOCl2(g) ΔH˚ = +51 - 98

                   answer:            ΔH˚ = -47kJ

Question 14

Based on the provided data, what is the change in Heat for the following reaction?
P4 + 3O2 = P4O6

P4O10 = P4O6 + 2O2 change in Heat: 1300 kJ
P4 + 5O2 = P4O10 change in Heat: -2940 kJ

a. -4240 kJ
b. -1640 kJ
c. -340 kJ
d. 1640 kJ
e. 4240 kJ

Answer 14

P4O10(s) → P4O6(s) + 2O2(g) ΔH˚ = +1300kJ

P4(s) + 5O2(g) → P4O10(s) ΔH˚ = -2940kJ

P4O10(s) + P4(s) + 35O2(g) → P4O6(s) + 2O2(g) + P4O10(s)

This reduces to the desired reaction:

P4(s) + 3O2(g) → P4O6(s) ΔH˚ = 1300 – 2940 = -1640kJ

Question 15

Based on the proided enthalpies of formation, what is the change in Heat for the following reaction?
2SO3 (g) = 2SO2 (g) + O2 (g)

SO3 -396 kJ
SO2 -297 kJ

a. -693 kJ
b. 99 kJ
c. 198 kJ
d. -1386 kJ
e. 693 kJ

Answer 15

198 kJ

products - reactants

but don’t count anything in its standard state… (see study guide)

Question 16

Based on the provided enthalpies of formation, what is the change in Heat for the following reaction?
2IBr (g) + Cl2 (g) = 2ICl (g) + Br2 (l)

IBr (g) 47 kJ
ICl (g) 18 kJ

a. -23 kJ
b. 59 kJ
c. 118 kJ
d. -46 kJ
e. -118 kJ

Answer 16

-46 kJ

Also recall that any element in its standard state has an enthalpy of formation of zero as does O2(g) in this problem.

Question 17

Based on the provided enthalpies of formation, what is the change in Heat for the following reaction?
2C2H2 (g) + 5O2 (g) = 4CO2 (g) + 2H2O (g)

C2H2 (g) 227 kJ
CO2 (g) -394 kJ
H2O (g) -242 kJ

a. -863 kJ
b. -409 kJ
c. 863 kJ
d. -2514 kJ
e. -1606 kJ

Answer 17

-2514 kJ

Also recall that any element in its standard state has an enthalpy of formation of zero as does O2(g) in this problem.

Question 18

Based on the provided enthalpies of formation, what is the change in Heat for the following reaction?
2Cu2O (s) + O2 (g) = 4 CuO (s)

Cu2O (s) -169 kJ
CuO (s) -157 kJ

a. -290 kJ
b. -12 kJ
c. 12 kJ
d. 290 kJ
e. -326 kJ

Answer 18

-290 kJ

Also recall that any element in its standard state has an enthalpy of formation of zero as does O2(g) in this problem.