# Thermochemistry Review

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Questions: 15 | Attempts: 4,520

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• 1.

• 2.

### The SI unit of energy is

• A.

Heat capacity.

• B.

Calorie.

• C.

Joule.

• D.

Enthalpy.

C. Joule.
Explanation
The SI unit of energy is joule. Energy is defined as the ability to do work or cause a change. The joule is the unit used to measure energy in the International System of Units (SI). It is named after James Prescott Joule, a British physicist who made significant contributions to the study of energy and heat. The joule is defined as the amount of energy transferred when a force of 1 newton is applied over a distance of 1 meter. It is widely used in physics and engineering to measure various forms of energy, such as mechanical, electrical, and thermal energy.

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• 3.

### How many calories are required to raise the temperature of 75.0 g of water from 20C to 50C?

• A.

2250 cal

• B.

3750 cal

• C.

75.0 cal

A. 2250 cal
Explanation
To calculate the amount of calories required to raise the temperature of a substance, we can use the equation Q = mcΔT, where Q is the heat energy, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature. In this case, the mass of water is given as 75.0 g, the specific heat capacity of water is approximately 1 cal/g°C, and the change in temperature is 50°C - 20°C = 30°C. Plugging these values into the equation, we get Q = (75.0 g)(1 cal/g°C)(30°C) = 2250 cal. Therefore, 2250 cal is the correct answer.

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• 4.

### When your body is warmed by an electric blanket during the winter, this process is said to be

• A.

Endothermic.

• B.

Exothermic.

• C.

Isothermic.

A. Endothermic.
Explanation
When your body is warmed by an electric blanket during the winter, it is considered endothermic because the heat is being absorbed by your body from an external source (the electric blanket). Endothermic processes involve the absorption of heat or energy from the surroundings, resulting in an increase in temperature. In this case, the electric blanket transfers heat to your body, helping to warm you up.

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• 5.

### A student mixes two water solutions with an initial temperature of 25.0C to form a final solution with a mass of 65.0 g at 30.0C. What is the heat change, in kJ, for this reaction?

• A.

325 kJ

• B.

272 kJ

• C.

1.36 kJ

C. 1.36 kJ
Explanation
The heat change for a reaction can be calculated using the equation: q = mcΔT, where q is the heat change, m is the mass of the solution, c is the specific heat capacity of water, and ΔT is the change in temperature. In this case, the mass of the solution is given as 65.0 g, and the change in temperature is 30.0C - 25.0C = 5.0C. The specific heat capacity of water is approximately 4.18 J/g°C. Using these values, we can calculate the heat change in joules: q = (65.0 g)(4.18 J/g°C)(5.0C) = 1361 J. Converting this to kJ gives 1.36 kJ, which matches the given answer.

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• 6.

### Given the equation Si(s) + 2Cl2(g) ------>SiCl2(g) ------>SiCl2(l) + 687 kJ, how much heat is produced when 106 g of Cl2 react?

• A.

513 kJ

• B.

360 kJ

• C.

180 kJ

A. 513 kJ
Explanation
In the given equation, it is stated that 687 kJ of heat is produced when Si(s) reacts with 2Cl2(g) to form SiCl2(l). Therefore, since the question asks for the heat produced when 106 g of Cl2 react, we can determine the amount of heat produced by using stoichiometry. From the balanced equation, we can see that 1 mole of Cl2 reacts with 687 kJ of heat. We can calculate the number of moles of Cl2 in 106 g using its molar mass, and then use the mole ratio to find the heat produced. The calculation results in 513 kJ of heat produced.

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• 7.

### A metal has a specific heat capacity of .899 Jg-1K-1 How much energy is required to raise the temperature of 2.00 kg of the metal by 80 K?

• A.

80 kJ

• B.

35.96 kJ

• C.

179800 kJ

• D.

143.84 J

• E.

143.84 kJ

E. 143.84 kJ
Explanation
The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 gram of the substance by 1 Kelvin. In this question, we are given the specific heat capacity of the metal (.899 Jg-1K-1) and the mass of the metal (2.00 kg). To find the amount of energy required to raise the temperature of the metal by 80 K, we can use the formula: Energy = specific heat capacity × mass × change in temperature. Plugging in the values, we get: Energy = .899 Jg-1K-1 × 2.00 kg × 80 K = 143.84 kJ. Therefore, the correct answer is 143.84 kJ.

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• 8.

### Which of the following is NOT a unit for heat?

• A.

Celsius

• B.

Calories

• C.

Joules

• D.

Kilocalories

A. Celsius
Explanation
Celsius is a unit for temperature, not heat. Heat is typically measured in units such as calories, joules, or kilocalories. Celsius is used to measure the temperature scale and represents the degree of hotness or coldness of an object or environment. It is not directly related to the amount of heat energy present.

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• 9.

### A metal has a specific heat capacity of .899 Jg-1K-1 How much energy is required to raise the temperature of 2.00 kg of the metal by 80 K?

• A.

80 kJ

• B.

35.96 kJ

• C.

179800 kJ

• D.

143.84 J

• E.

143.84 kJ

E. 143.84 kJ
Explanation
The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 gram of the substance by 1 Kelvin. In this question, we are given the specific heat capacity of the metal (.899 Jg-1K-1) and the mass of the metal (2.00 kg). To find the amount of energy required to raise the temperature of the metal by 80 K, we can use the formula: energy = mass * specific heat capacity * change in temperature. Plugging in the given values, we get: energy = 2.00 kg * .899 Jg-1K-1 * 80 K = 143.84 kJ. Therefore, the correct answer is 143.84 kJ.

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• 10.

### Which of the following is NOT a unit for heat?

• A.

Celsius

• B.

Calories

• C.

Joules

• D.

Kilocalories

A. Celsius
Explanation
Celsius is a unit for temperature, not heat. Heat is measured in calories, joules, and kilocalories, but Celsius is a scale used to measure temperature.

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• 11.

### A piece of aluminum (3.6 g) is heated from 20oC to 30oC. If the specific heat of aluminum os 0.897 J/goC, how much heat energy was absorbed?

• A.

322.92 J

• B.

32.292 J

• C.

3.2292

• D.

3.6 J

B. 32.292 J
Explanation
(heat absorbed q) = (3.6 g) (10 C) (0.0897 J/g C)

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• 12.

### A 150.0 g sample of metal at 75.0 C is added to 150.0 g of H2O at 15.0 C.  The temperature of the water rises to 18.3 C.  Calculate the heat capacity of the metal, assuming that all the heat lost by the metal is gained by the water.  The heat capacity of water is 4.18 J/g C

• A.

0.22 J/ g C

• B.

0.25 J/ g C

• C.

0.23 J/ g C

• D.

0.48 J/ g C

• E.

0.43 J/ g C

B. 0.25 J/ g C
Explanation
The heat absorbed by the water = q= smΔT = 2100 J. Heat released from the metal is = heat gained by the water. Heat released = -q = smΔT.

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• 13.

### What do we call the heat content of a system

• A.

Entropy

• B.

Heat

• C.

Enthalpy

• D.

Temeprature

C. Enthalpy
Explanation
Enthalpy refers to the heat content of a system. It is a thermodynamic property that includes both the internal energy of a system and the product of its pressure and volume. Enthalpy is often used to measure heat flow in chemical reactions or phase changes. It is represented by the symbol H and is measured in units of energy, such as joules or calories.

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• 14.

### A 150.0 g sample of metal at 75.0 C is added to 150.0 g of H2O at 15.0 C.  The temperature of the water rises to 18.3 C.  Calculate the heat capacity of the metal, assuming that all the heat lost by the metal is gained by the water.  The heat capacity of water is 4.18 J/g C

• A.

0.22 J/ g C

• B.

0.25 J/ g C

• C.

0.23 J/ g C

• D.

0.48 J/ g C

• E.

0.43 J/ g C

C. 0.23 J/ g C
Explanation
Certainly! Here's a simplified format:

To calculate the heat capacity of the metal:

1. For the water:
- Mass of water (m_water) = 150.0 g
- Specific heat capacity of water (c_water) = 4.18 J/g°C
- Change in temperature of water (ΔT_water) = 18.3°C - 15.0°C = 3.3°C
- Calculate Q_water = m_water * c_water * ΔT_water

2. For the metal:
- Mass of metal (m_metal) = 150.0 g
- Change in temperature of metal (ΔT_metal) = 75.0°C - 18.3°C = 56.7°C
- Calculate c_metal using the equation:
c_metal = (m_water * c_water * ΔT_water) / (m_metal * ΔT_metal)

3. Calculate c_metal:
- c_metal ≈ 0.2286 J/g°C

So, the heat capacity of the metal is approximately 0.2286 J/g°C, which is rounded off to 0.23 J/g°C.

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• 15.

### True or false:  The change in enthalpy for an exothermic process is positive.

• A.

True

• B.

False

B. False
Explanation
The change in enthalpy for an exothermic process is negative, not positive. In an exothermic process, heat is released to the surroundings, resulting in a decrease in the system's enthalpy. Therefore, the correct answer is false.

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• 16.

### Sodium hydrogen carbonate decomposes to form sodium carbonate, water, and carbon dioxide gas.  The heat of reaction for this decomposition is 129 kJ.  What is the change in enthalpy when 2.24 mol of sodium hydrogen carbonate react?

• A.

5.7 kJ

• B.

144 kJ

• C.

-898 kJ

• D.

-144 kJ

B. 144 kJ
Explanation
The change in enthalpy when 2.24 mol of sodium hydrogen carbonate decomposes can be calculated using the heat of reaction. Since the heat of reaction is given as 129 kJ, and 2.24 mol of sodium hydrogen carbonate is reacting, the change in enthalpy can be calculated by multiplying the heat of reaction by the number of moles of the reactant. Therefore, the change in enthalpy is 129 kJ/mol x 2.24 mol = 289.76 kJ. However, since the question asks for the change in enthalpy, the answer should have the opposite sign, resulting in -289.76 kJ. The closest option to this value is -144 kJ, which is the correct answer.

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• Current Version
• Sep 12, 2023
Quiz Edited by
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• May 13, 2014
Quiz Created by
Jzajac

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