Textbook Question
(b) Is this process endothermic or exothermic?
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Ch.5 - Thermochemistry
Chapter 5, Problem 58a
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.
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Identify the chemical formula for phenol, which is C_6H_5OH.
Write the general form of a combustion reaction: C_xH_yO_z + O_2 -> CO_2 + H_2O.
Balance the carbon atoms: C_6H_5OH + O_2 -> 6CO_2 + H_2O.
Balance the hydrogen atoms: C_6H_5OH + O_2 -> 6CO_2 + 3H_2O.
Balance the oxygen atoms by adjusting the O_2 molecules: C_6H_5OH + 7.5O_2 -> 6CO_2 + 3H_2O.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Combustion Reaction
A combustion reaction is a chemical process in which a substance (typically a hydrocarbon) reacts with oxygen to produce carbon dioxide, water, and energy. In the case of phenol (C6H5OH), the balanced equation will show phenol reacting with oxygen to yield carbon dioxide and water, illustrating the transformation of chemical energy into thermal energy.
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Combustion Apparatus
Calorimetry
Calorimetry is the science of measuring the heat of chemical reactions or physical changes. In this scenario, a bomb calorimeter is used to measure the heat released during the combustion of phenol. The temperature change observed in the calorimeter allows for the calculation of the heat of combustion, which is essential for understanding the energy changes involved in the reaction.
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Heat Capacity
Heat capacity is the amount of heat required to change the temperature of a substance by one degree Celsius. In this question, the total heat capacity of the bomb calorimeter is given as 11.66 kJ/°C, which indicates how much energy is absorbed by the calorimeter for each degree of temperature increase. This value is crucial for calculating the total heat released during the combustion of phenol based on the observed temperature change.
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Related Practice
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. b. What is the heat of combustion per gram of phenol?
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?
Textbook Question
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.