[PPT]Heat and Energy - Kennesaw State Universityksuweb.kennesaw.edu/.../2.5_Specific_Heat.ppt · Web viewTitle Heat and Energy Author Karen Timberlake Last modified by Proof Proof

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 3

Specific Heats of Some Substances

© 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 6

Guide to Calculating Specific Heat

© 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 10

Guide to Calculations Using Specific Heat

© 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.

© 2013 Pearson Education, Inc. Chapter 2, Section 5 17

How many kilojoules are needed to raise thetemperature of 325 g of water from 15.0 C to 77.0 C?Step 4 Substitute given values and solve, making sure the units cancel.

Solution