Textbook Question
When a 6.50-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter (Figure 5.18), the temperature rises from 21.6 to 37.8 °C (a) Calculate the quantity of heat (in kJ) released in the reaction.
Ch.5 - Thermochemistry
Chapter 5, Problem 57
A 1.50-g sample of quinone (C6H4O2) is burned in a bomb calorimeter whose total heat capacity is 8.500 kJ/°C. The temperature of the calorimeter increases from 25.00 to 29.49°C. (b) What is the heat of combustion per gram of quinone and per mole of quinone?
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Calculate the total heat absorbed by the calorimeter using the formula: \( q = C_{cal} \times \Delta T \), where \( C_{cal} \) is the heat capacity of the calorimeter and \( \Delta T \) is the change in temperature.
Determine the change in temperature \( \Delta T \) by subtracting the initial temperature from the final temperature: \( \Delta T = 29.49\, ^\circ\text{C} - 25.00\, ^\circ\text{C} \).
Substitute the values of \( C_{cal} \) and \( \Delta T \) into the formula to find the total heat \( q \) absorbed by the calorimeter.
Calculate the heat of combustion per gram of quinone by dividing the total heat \( q \) by the mass of the quinone sample (1.50 g).
Calculate the molar mass of quinone (C6H4O2) and use it to convert the heat of combustion per gram to per mole by multiplying the heat per gram by the molar mass.
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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 quinone. The heat capacity of the calorimeter allows us to calculate the total heat absorbed by the calorimeter based on the temperature change observed.
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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 per gram or per mole. To find the heat of combustion for quinone, we will use the total heat absorbed by the calorimeter and relate it to the mass of quinone burned.
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Molar Mass
Molar mass is the mass of one mole of a substance, expressed in grams per mole. For quinone (C6H4O2), the molar mass is calculated by summing the atomic masses of its constituent elements. This value is essential for converting the heat of combustion from a per gram basis to a per mole basis, allowing for a comprehensive understanding of the energy released during combustion.
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Related Practice
Textbook Question
When a 6.50-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter (Figure 5.18), the temperature rises from 21.6 to 37.8 °C (b) Using your result from part (a), calculate H (in kJ/mol KOH) for the solution process. Assume that the specific heat of the solution is the same as that of pure water.
Textbook Question
(b) Is this process endothermic or exothermic?
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Textbook Question
A 1.50-g sample of quinone (C6H4O2) is burned in a bomb calorimeter whose total heat capacity is 8.500 kJ/°C. The temperature of the calorimeter increases from 25.00 to 29.49 °C. (a) Write a balanced chemical equation for the bomb calorimeter reaction.
Textbook Question
A 2.20-g sample of phenol (C6H5OH) was burned in a bomb calorimeter whose total heat capacity is 11.90 kJ/°C. The temperature of the calorimeter plus contents increased from 21.50 to 27.50 °C. (a) Write a balanced chemical equation for the bomb calorimeter reaction.
Textbook Question
A 2.20-g sample of phenol (C6H5OH) was burned in a bomb calorimeter whose total heat capacity is 11.90 kJ/°C. The temperature of the calorimeter plus contents increased from 21.50 to 27.50 °C. (b) What is the heat of combustion per mole of phenol?