   # A coffee-cup calorimeter initially contains 125 g water at 24.2°C. Potassium bromide (10.5 g), also at 24.2°C, is added to the water, and after the KBr dissolves, the final temperature is 21.1°C. Calculate the enthalpy change for dissolving the: salt in J/g and kJ/mol. Assume that the specific heat capacity of the solution is 4.18 J/°C · g and that no heat is transferred to the surroundings or to the calorimeter. ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 7, Problem 61E
Textbook Problem
43 views

## A coffee-cup calorimeter initially contains 125 g water at 24.2°C. Potassium bromide (10.5 g), also at 24.2°C, is added to the water, and after the KBr dissolves, the final temperature is 21.1°C. Calculate the enthalpy change for dissolving the: salt in J/g and kJ/mol. Assume that the specific heat capacity of the solution is 4.18 J/°C · g and that no heat is transferred to the surroundings or to the calorimeter.

Interpretation Introduction

Interpretation: The enthalpy change for dissolving the KBr salt in Water has to be calculated.

Concept Introduction: The heat capacity C is defined as the ratio of heat absorbed and temperature change. It can be given by,

C = heat absorbed/temperature change

• Require heat of an one gram of substance raise to its temperature by one degree Celsius is called specific heat capacity.

Absorbed heat (J) = Specific heat capacity ×Temperature change(c)×mass of substance (g)...(1)

For in above equation heat is:

q= s×M×T....(2)

S is specific heat capacity (J/°C·g.)

q is heat (J)

M is mass of sample (g)

T is temperature change (C)

For the process no heat loss to the surroundings means then the heat is

q (absorbed) =-q (released).....(3)

### Explanation of Solution

Explanation

Given data

Water weight is 125g

Initial temperature of solution is 24.2C

Mass of potassium bromide is 10.5g

Final temperature of solution is 21.1 C

specific heat capacity of the solution is 4.18 J/C·g

The final weight of solution is 125g +10.5 = 135.5g

Mass of g KBr is 119.0g

To determine: Heat lost by solution

Heat lost by solution is equal to heat gained by KBr

Heat lost by solution  = 4.18×135.5×(24.2-21...

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