Ch.5 - Thermochemistry

Problem 55a

Previous problem

Next problem

Chapter 5, Problem 55a

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.

Verified step by step guidance

Identify the mass of the solution, which is the sum of the mass of sodium hydroxide and the mass of water.

Use the specific heat capacity of water (4.18 J/g°C) to calculate the heat absorbed by the solution using the formula: q = m * c * ΔT, where m is the mass of the solution, c is the specific heat capacity, and ΔT is the change in temperature.

Calculate the change in temperature (ΔT) by subtracting the initial temperature from the final temperature.

Convert the calculated heat from joules to kilojoules by dividing by 1000.

Since the heat is released by the reaction, express the final answer as a negative value to indicate exothermic reaction.

Verified Solution

Video duration:

This video solution was recommended by our tutors as helpful for the problem above.

Was this helpful?

Key Concepts

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

Heat Transfer and Calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes. In this context, the heat released when sodium hydroxide dissolves in water can be calculated using the formula q = mcΔT, where q is the heat absorbed or released, m is the mass of the solution, c is the specific heat capacity of water, and ΔT is the change in temperature.

Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. For water, this value is approximately 4.18 J/g°C. Understanding this concept is crucial for calculating the heat change in the calorimeter when the sodium hydroxide dissolves and the temperature of the water increases.

Dissolution and Exothermic Reactions

The dissolution of sodium hydroxide in water is an exothermic process, meaning it releases heat. This release of heat causes the temperature of the solution to rise, which is a key observation in calorimetry experiments. Recognizing that the dissolution process is exothermic helps in understanding the overall energy changes involved in the reaction.

Recommended video:

Guided course

02:38

Endothermic & Exothermic Reactions

Previous problem

Next problem

Related Practice

Textbook Question

The specific heat of octane, C₈H₁₈(l), is 2.22 J•g/K. (b) Which will require more heat, increasing the temperature of 1 mol of C₈H₁₈(l), by a certain amount or increasing the temperature of 1 mol of H₂O(l) by the same amount?

2232

views

Textbook Question

Consider the data about gold metal in Exercise 5.26(b). (b) Suppose that the same amount of heat is added to two 10.0-g blocks of metal, both initially at the same temperature. One block is gold metal, and one is iron metal. Which block will have the greater rise in temperature after the addition of the heat?

667

views

Textbook Question

Consider the data about gold metal in Exercise 5.26(b). (c) What is the molar heat capacity of Au(s)?

588

views

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.

(b) Is this process endothermic or exothermic?

487

views

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. (b) What is the heat of combustion per gram of quinone and per mole of quinone?

1448

views