# CHEM126 – CHAPTER 17 – BASIC HOMEWORK / THERMODYNAMICS I

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### Question 1

How much energy in kJ is required to heat a calorimeter whose heat capacity is 510.0 J/oC from 23.5oC to 53.0oC?

Heat capacity calculation ### Explanation

Don’t forget to change to kJ.

### Question 2

What is the heat capacity of a calorimeter in J/oC if 120.3 J of heat raises its temperature by 5.0 oC? ### Question 3

What is the heat capacity of 0.83 kg of water in J/oC? The specific heat of water is 4.184 J/(goC).

Specific heat definition and example ### Question 4

The specific heat of iron is 0.45 J/(goC). How much heat in J is added to a 9.24 g iron nail to raise its temperature from 22oC to 478.6oC?

Specific heat 2nd example ### Question 5

A bowl of 192 g of water is placed in a microwave oven that puts out 642 watts (J/s). How long would it take in seconds to increase the temperature of the water from 12.0oC to 55.2oC?

Help given in feedback. ### Explanation

1. Find how many J are needed.
2. Convert J to sec. For example, suppose the microwave puts out 500 watts that is 500 J/s. To convert J to s do you multiple by (500 J)/s or 1 s/(500 J)?

### Question 6

285.5 g of water is in a Styrofoam calorimeter of negligible heat capacity. The initial T of the water is 21.4oC. After 276.0 g of an unknown compound at 75.2oC is added, the equilibrium T is 30.8oC. What is the specific heat of the unknown compound in J/(goC)?

Specific heat 3rd example ### Question 7

What is the approximate specific heat in J/(goC) of a metal whose M.W. is 58.5 g/mol?

Law of Dulong et Petit ### Question 8

Match corresponding quantities.

Energy defined and kinds of energy

Conservation of energy Energy Photon energy Kinetic energy Potential energy ### Question 9

4000 J of heat are added to a system. The surroundings do 1600 J of work on system. What is ΔE in J?

Energy calculation ### Question 10

6100 J of heat are extracted from a system. The system does 1300 J of work on the surroundings. What is ΔE in J? ### Question 11

The temperature of the system is fixed. 274 J of heat are added to the system. What is the work in J done on the system?

Help given in feedback. ### Explanation

The following two equations are always true: ΔE = q + w and ΔE = CVΔT where CV is the heat capacity at constant volume. The second equation says that if the temperature of a system increases its internal energy, E, increases. What is ΔE if the temperature is constant?

### Question 12

The work done on a system for a certain adiabatic process is -255 J. What is ΔE in J? ### Question 13

A person takes a complicated switchback trail to the top of a mountain. For which of the following cases would the person end up with the same potential energy or height?

Examples of state functions

Select one or more:   ### Explanation

All must be correct for credit.

### Question 14

A process takes place at constant pressure. The volume changes and the temperature increases by 94.7oC. The heat capacity of the system at constant volume, CV, is 475.3 kJ/oC. What is ΔE in kJ?

Help given in feedback. ### Explanation

Because E is a state function, no matter how it is correctly calculated you will get the same answer. Thus, even though the volume is not constant, you can use ΔE = CVΔT.

### Question 15

For which of the following is the enthalpy of formation, ΔHfo = 0?

Enthalpy of formation of elementsSelect one or more:    h. C (diamond state)

### Explanation

graphite state is more stable at STP (standard pressure and temperature)

### Question 16

For which of the following reactions is the enthalpy change in the reaction, ΔHrxno, equal to ΔHfo for NH4OH(s)?

The Enthalpy of formation of a compound is given by the reaction where all the reactants are elements in their standard state and the product is the desired compound.

Select one: ### Question 17

Calculate the enthalpy of reaction for the following reaction:

2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)

ΔHfo(Fe2O3(s)) = -824.2 kJ/mol
ΔHfo(C(s)) = ?
ΔHfo(Fe(s)) = ?
ΔHfo(CO2(g)) = -393.5 kJ/mol

### Question 18

he previous reaction is

Exothermic and endothermic reactions
Select one: ### Question 19

Calculate the enthalpy of reaction for the following reaction:

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

ΔHfo(Fe2O3(s)) = -824.2 kJ/mol
ΔHfo(CO(g)) = -110.5
ΔHfo(Fe(s)) = ?
ΔHfo(CO2(g)) = -393.5 kJ/mol ### Question 20

The previous reaction is

Select one: 