CHEM126 – CHAPTER 17 – BASIC HOMEWORK / THERMODYNAMICS I

 

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
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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?

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Explanation

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

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Explanation

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

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Explanation

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?

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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

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Explanation

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

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Explanation

Question 8

 

Match corresponding quantities.

Energy defined and kinds of energy

Conservation of energy

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Energy

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Photon energy

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Kinetic energy

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Potential energy

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Explanation

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

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Explanation

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?

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Explanation

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?

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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?

Adiabatic process defined
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Explanation

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:chem126-17bt - Fluff Butt Reviews chem126-17bt - Fluff Butt Reviews
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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?

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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:

 

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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:




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Explanation

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

Explanation

Question 18

he previous reaction is

Exothermic and endothermic reactions
Select one:
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Explanation

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

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Explanation

Question 20

The previous reaction is

 

Select one:

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Explanation