Q: Which equation correctly relates the heat absorbed by the solution in a coffee-cup calorimeter?

$$q_r = -m_{H_2O} \times C_{H_2O} \times \Delta T_{H_2O}$$

Question 1

Which of the following statements correctly distinguishes between extensive and intensive properties in thermochemistry?

Accepted Answer

Extensive properties depend on the amount of substance present, while intensive properties do not.

Question 2

A reaction is carried out in a bomb calorimeter and a coffee-cup calorimeter with the same amount of reactant. The measured heat in the bomb calorimeter is $$q_n = -12.5 kJ $$and in the coffee-cup calorimeter is $$q_p = -11.8 kJ. $$Which value corresponds to the bomb calorimeter?

Accepted Answer

$$q_n = -12.5 kJ$$

Question 3

Given the reaction $$2HF(g) \rightarrow H_2$(g) + F_2$(g)$$ with $$\Delta_r H = +546 kJ$$ $$\cdot$$ mol$$^{-1}$$, what is the enthalpy change for the reverse reaction?

Accepted Answer

$$\Delta_r H = -546 kJ$$ $$\cdot$$ mol$$^{-1}$$

Question 4

In a constant pressure calorimetry experiment, 0.0400 mol of HCl(aq) is mixed with 0.0450 mol of NH$$_3OH(aq). $$Which is the limiting reagent?

Accepted Answer

HCl(aq)

Question 5

Which equation correctly relates the heat absorbed by the solution in a coffee-cup calorimeter?

Accepted Answer

$$q_r = -m_{H_2O} 	imes C_{H_2O} 	imes \Delta T_{H_2O}$$

Question 6

If the enthalpy of vaporization of ethanol is $$38.56 kJ$$ $$\cdot$$ mol$$^{-1}$$, what is the enthalpy change when 2 moles of ethanol condense?

Accepted Answer

$$\Delta H = -77.12 kJ$$

Question 7

Which of the following is the correct thermochemical equation for the enthalpy of formation of KBr(s)?

Accepted Answer

$$K(s) + \frac{1}{2} Br_2$(l) \rightarrow KBr(s)$$

Question 8

For the reaction $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l)$$, $$\Delta_r H = -572 kJ$$ $$\cdot$$ mol$$^{-1}. $$What is $$\Delta_r H$$ for $$H_2(g$$) + \frac{1}{2} $$O_2(g$$) \rightarrow H_2O(l)$$?

Accepted Answer

$$\Delta_r H = -286 kJ$$ $$\cdot$$ mol$$^{-1}$$

Question 9

Which of the following best describes Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the pathway taken, and can be calculated by summing the enthalpy changes of individual steps.

Question 10

A chemical reaction is reversed. What happens to the sign of $$\Delta_r H$$?

Accepted Answer

The sign of $$\Delta_r H is $$reversed.

Question 11

Which of the following reactions represents the enthalpy of vaporization?

Accepted Answer

$$C_6H_6(l) \rightarrow C_6H_6(g)$$

Question 12

If a reaction produces more moles of gas than it consumes, how does $$\Delta_r H$$ compare to $$\Delta_r U$$?

Accepted Answer

$$\Delta_r H \u003e \Delta_r U$$

Question 13

Which formula is used to calculate the enthalpy change per mole in a calorimetry experiment?

Accepted Answer

$$\Delta_r H = \frac{q_{cal}}{n}$$

Question 14

A coffee-cup calorimeter contains 250 g of water. The temperature rises from 23.92$$^\circC to 26.07$^\circC. $$What is the value of $$\Delta T$$?

Accepted Answer

$$\Delta T = 2.15^\circC$$

Question 15

Which of the following is true about the enthalpy change for the reaction $$2H_2O(l) \rightarrow 2H_2(g) + O_2$(g) if$$ $$\Delta_r H$$ for $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(l) is$$ $$-572 kJ$$ $$\cdot$$ mol$$^{-1}$$?

Accepted Answer

$$\Delta_r H = +572 kJ$$ $$\cdot$$ mol$$^{-1}$$

Question 16

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction can be calculated by adding the enthalpy changes of multiple reactions that sum to the overall reaction.

Question 17

If the stoichiometric coefficient of a reaction is halved, what happens to $$\Delta_r H$$?

Accepted Answer

$$\Delta_r H is $$halved.

Question 18

Which of the following best describes the enthalpy of fusion?

Accepted Answer

The enthalpy change when a solid melts to become a liquid.

Chapter 6.4: Thermochemistry – Enthalpy, Calorimetry, and Stoichiometry

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