Q: Given the reaction: $$2 \mathrm{CH}_6\mathrm{N}_2 (l) + 5 \mathrm{O}_2 (g) \rightarrow 2 \mathrm{N}_2 (g) + 2 \mathrm{CO}_2 (g) + 6 \mathrm{H}_2\mathrm{O} (l)$$, what is the heat of reaction per mole of $$\mathrm{CH}_6\mathrm{N}_2 if$$ $$4.00 \ \mathrm{g} is $$combusted and the calorimeter absorbs $$113.013 \ \mathrm{kJ} of $$heat?

$$-1.30 \times 10^3$ \ \mathrm{kJ/mol}$$

Question 1

Which of the following best describes the purpose of a calorimeter in a chemical reaction?

Accepted Answer

To measure the change in enthalpy ($$\Delta H) by $$quantifying heat flow from the system to the surroundings.

Question 2

What is the correct formula for calculating the heat capacity ($$C) of a $$substance?

Accepted Answer

$$C = \dfrac{q}{\Delta T}$$

Question 3

A student adds 100 g of water to a calorimeter and heats it from 20.0°C to 30.0°C. If the specific heat of water is $$4.184 \ \mathrm{J/g\ ^\circ C}$$, how much heat ($$q) $$was absorbed by the water?

Accepted Answer

$$q = 4,184 \ \mathrm{J}$$

Question 4

Which of the following statements about heat capacity and specific heat is TRUE?

Accepted Answer

Heat capacity depends on the amount of substance, while specific heat is an intensive property.

Question 5

Given the reaction: $$2 \mathrm{CH}_6\mathrm{N}_2 (l) + 5 \mathrm{O}_2 (g) \rightarrow 2 \mathrm{N}_2 (g) + 2 \mathrm{CO}_2 (g) + 6 \mathrm{H}_2\mathrm{O} (l)$$, what is the heat of reaction per mole of $$\mathrm{CH}_6\mathrm{N}_2 if$$ $$4.00 \ \mathrm{g} is $$combusted and the calorimeter absorbs $$113.013 \ \mathrm{kJ} of $$heat?

Accepted Answer

$$-1.30 	imes 10^3$ \ \mathrm{kJ/mol}$$

Question 6

If the temperature of a calorimeter increases by $$14.50 ^\circ \mathrm{C}$$ and its heat capacity is $$7.794 \ \mathrm{kJ}/^\circ \mathrm{C}$$, what is the total heat absorbed by the calorimeter?

Accepted Answer

$$113.013 \ \mathrm{kJ}$$

Question 7

Which equation correctly defines specific heat capacity ($$C_s$$)?

Accepted Answer

$$C_s = \dfrac{q}{m \Delta T}$$

Question 8

A bomb calorimeter is used to measure the enthalpy change of a combustion reaction. Which of the following is a key assumption in this experiment?

Accepted Answer

No heat is lost to the surroundings; all heat is absorbed by the calorimeter.

Question 9

If $$1 \ \mathrm{cal} = 4.184 \ \mathrm{J}$$, how much energy in joules is required to raise the temperature of $$1.00 \ \mathrm{g} of $$water by $$1 ^\circ \mathrm{C}$$?

Accepted Answer

$$4.184 \ \mathrm{J}$$

Question 10

A student performs a calorimetry experiment and finds that $$q_{surroundings} = 113.013 \ \mathrm{kJ}. $$What is the value of $$q_{system}$$?

Accepted Answer

$$-113.013 \ \mathrm{kJ}$$

Question 11

Which of the following would increase the heat capacity of a calorimeter?

Accepted Answer

Increasing the mass of the calorimeter.

Question 12

A reaction in a calorimeter causes the temperature to decrease. What does this indicate about the reaction?

Accepted Answer

The reaction is endothermic; it absorbs heat from the surroundings.

Question 13

Which of the following is the correct unit for specific heat capacity ($$C_s$$)?

Accepted Answer

$$\mathrm{J/g\ ^\circ C}$$

Question 14

A sample of $$4.00 \ \mathrm{g}$$ methylhydrazine ($$\mathrm{CH}_6\mathrm{N}_2) is $$combusted in a calorimeter. If the molar mass of methylhydrazine is $$46.1 \ \mathrm{g/mol}$$, how many moles are combusted?

Accepted Answer

$$0.08677 \ \mathrm{mol}$$

Question 15

Which of the following best explains why Styrofoam cups are used in a simple calorimeter?

Accepted Answer

They act as thermal insulators, minimizing heat exchange with the environment.

Question 16

If a calorimeter has a heat capacity of $$7.794 \ \mathrm{kJ}/^\circ \mathrm{C}$$ and absorbs $$113.013 \ \mathrm{kJ} of $$heat, what is the temperature change ($$\Delta T$$)?

Accepted Answer

$$14.50 ^\circ \mathrm{C}$$

Question 17

Which of the following is NOT a direct application of calorimetry?

Accepted Answer

Measuring the pH of a solution.

Question 18

A student calculates the heat of reaction for a combustion experiment and gets a positive value. What does this indicate?

Accepted Answer

The reaction is endothermic; heat is absorbed by the system.

Question 19

Which of the following would result in a lower calculated specific heat for a substance, assuming all other variables are constant?

Accepted Answer

Decreasing the amount of heat transferred.

Calorimetry: Measuring Heat Changes in Chemical Reactions

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