A 1.800-g sample of phenol (C6H5OH) was burned in a bomb calorimeter whose total heat capacity is 11.66 kJ/°C. The temperature of the calorimeter plus contents increased from 21.36 to 26.37 °C. b. What is the heat of combustion per gram of phenol?

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Calculate the temperature change (\( \Delta T \)) of the calorimeter by subtracting the initial temperature from the final temperature: \( \Delta T = 26.37 \, ^\circ\text{C} - 21.36 \, ^\circ\text{C} \).

Use the formula for heat absorbed by the calorimeter: \( q = C_{cal} \times \Delta T \), where \( C_{cal} \) is the heat capacity of the calorimeter (11.66 kJ/°C) and \( \Delta T \) is the temperature change calculated in the previous step.

Determine the total heat released by the combustion of the phenol sample, which is equal to the heat absorbed by the calorimeter (\( q \)).

Calculate the heat of combustion per gram of phenol by dividing the total heat released (\( q \)) by the mass of the phenol sample (1.800 g).

Express the result in kJ/g, which represents the heat of combustion per gram of phenol.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes. In this context, a bomb calorimeter is used to measure the heat released during the combustion of phenol. The heat capacity of the calorimeter allows us to calculate the total heat absorbed by the calorimeter from the temperature change observed.

Heat of Combustion

The heat of combustion is the amount of energy released when a substance is completely burned in oxygen. It is typically expressed in joules or kilojoules per gram. To find the heat of combustion per gram of phenol, we need to determine the total heat released during the combustion and then divide that by the mass of the phenol sample.

Temperature Change and Heat Transfer

The temperature change in a calorimeter is directly related to the heat transfer that occurs during a reaction. The formula used is Q = C × ΔT, where Q is the heat absorbed, C is the heat capacity, and ΔT is the change in temperature. This relationship allows us to calculate the total heat released from the combustion of phenol, which is essential for determining the heat of combustion per gram.

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Textbook Question

A 2.200-g sample of quinone (C₆H₄O₂) is burned in a bomb calorimeter whose total heat capacity is 7.854 kJ/°C. The temperature of the calorimeter increases from 23.44 to 30.57 °C. (a) What is the heat of combustion per gram of quinone?

Textbook Question

A 2.200-g sample of quinone (C₆H₄O₂) is burned in a bomb calorimeter whose total heat capacity is 7.854 kJ/°C. The temperature of the calorimeter increases from 23.44 to 30.57 °C. b. What is the heat of combustion per mole of quinone?

Textbook Question

A 1.800-g sample of phenol (C₆H₅OH) was burned in a bomb calorimeter whose total heat capacity is 11.66 kJ/°C. The temperature of the calorimeter plus contents increased from 21.36 to 26.37 °C. a. Write a balanced chemical equation for the bomb calorimeter reaction.

Textbook Question

Under constant-volume conditions, the heat of combustion of benzoic acid (C₆H₅COOH) is 26.38 kJ/g. A 2.760-g sample of benzoic acid is burned in a bomb calorimeter. The temperature of the calorimeter increases from 21.60 to 29.93 °C. c. Suppose that in changing samples, a portion of the water in the calorimeter were lost. In what way, if any, would this change the heat capacity of the calorimeter?

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Consider the following hypothetical reactions: A → B ΔH = +30 kJ B → C ΔH = +60 kJ (b) Construct an enthalpy diagram for substances A, B, and C, and show how Hess's law applies.

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