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General, Organic, and Biological Chemistry
Fourth EditionKaren Timberlake
2.5Specific Heat
Chapter 2Energy and Matter
© 2013 Pearson Education, Inc.Lectures
© 2013 Pearson Education, Inc. Chapter 2, Section 5 2
Specific Heat
Specific heat is different for different substances. is the amount of heat that raises the temperature of 1 g of a substance by 1 C. is represented by the equation,
where ΔT = the change in temperature. in the SI system, has units of J/g C. in the metric system, has units of cal/g C.
© 2013 Pearson Education, Inc. Chapter 2, Section 5 4
Learning Check
1. If the same amount of heat is added, what will occur in a substance with a lower specific heat?
A. a smaller increase in temperature B. a greater increase in temperature
2. When ocean water warms, what happens to the surrounding air? A. cools B. warms C. stays the same
© 2013 Pearson Education, Inc. Chapter 2, Section 5 5
Solution
1. If the same amount of heat is added, what will occur in a substance with a low, specific heat?B. a greater increase in temperature
2. When ocean water warms, what happens to the surrounding air? A. cools
© 2013 Pearson Education, Inc. Chapter 2, Section 5 7
Calculating Specific Heat
What is the specific heat of a metal if 24.8 g absorbs65.7 cal of energy and the temperature rises from20.2 C to 24.5 C? Step 1 State the given and needed quantities.
Analyze the Problem.Given Need24.8 g 65.7 calΔT = 20.2 C to 24.5 C
© 2013 Pearson Education, Inc. Chapter 2, Section 5 8
Calculating Specific Heat
What is the specific heat of a metal if 24.8 g absorbs65.7 cal of energy and the temperature rises from20.2 C to 24.5 C? Step 2 Write the relationship for specific heat.
Step 3 Set up the problem to calculate SH.
© 2013 Pearson Education, Inc. Chapter 2, Section 5 9
Heat Equation
Rearranging the specific heat expression gives theheat equation:
The amount of heat lost or gained by a substance iscalculated from the mass of substance (g), the temperature change (T), or the specific heat of the substance (cal/g C) or
(J/g C).
© 2013 Pearson Education, Inc. Chapter 2, Section 5 11
A hot-water bottle contains 750 g of water at 65 C. If the water cools to body temperature (37 C), how many calories of heat could be transferred to sore muscles?Step 1 State the given and needed quantities.
Analyze the Problem.
Sample Calculation for using Specific Heat
Given Need Calories of heat
transferred
© 2013 Pearson Education, Inc. Chapter 2, Section 5 12
A hot-water bottle contains 750 g of water at 65 C. If the water cools to body temperature (37 C), how many calories of heat could be transferred to sore muscles?Step 2 Calculate the temperature change (T).
Step 3 Write the heat equation.
Sample Calculation for using Specific Heat
© 2013 Pearson Education, Inc. Chapter 2, Section 5 13
A hot-water bottle contains 750 g of water at 65 C. If the water cools to body temperature (37 C), how many calories of heat could be transferred to sore muscles?Step 4 Substitute in the given values and solve, making sure units cancel.
Sample Calculation for using Specific Heat
© 2013 Pearson Education, Inc. Chapter 2, Section 5 14
Learning Check
How many kilojoules are needed to raise thetemperature of 325 g of water from 15.0 C to 77.0 C?A. 20.2 kJB. 84.3 kJC. 105 kJ
© 2013 Pearson Education, Inc. Chapter 2, Section 5 15
Solution
How many kilojoules are needed to raise thetemperature of 325 g of water from 15.0 C to 77.0 C?Step 1 State the given and needed data.
Analyze the Problem.Given Need Kilojoules of
heat needed
© 2013 Pearson Education, Inc. Chapter 2, Section 5 16
Solution
How many kilojoules are needed to raise thetemperature of 325 g of water from 15.0 C to 77.0 C?Step 2 Calculate the temperature change T.
Step 3 Write the heat equation.