General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 2.5 Specific Heat Chapter 2 Energy 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 absorbs 65.7 cal of energy and the temperature rises from 20.2  C to 24.5  C? Step 1 State the given and needed quantities. Analyze the Problem. GivenNeed 24.8 g 65.7 cal ΔT = 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 absorbs 65.7 cal of energy and the temperature rises from 20.2  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 the heat equation: The amount of heat lost or gained by a substance is calculated 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 GivenNeed 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 the temperature of 325 g of water from 15.0  C to 77.0  C? A kJ B kJ C. 105 kJ

© 2013 Pearson Education, Inc. Chapter 2, Section 5 15 Solution How many kilojoules are needed to raise the temperature of 325 g of water from 15.0  C to 77.0  C? Step 1 State the given and needed data. Analyze the Problem. GivenNeed Kilojoules of heat needed

© 2013 Pearson Education, Inc. Chapter 2, Section 5 16 Solution How many kilojoules are needed to raise the temperature 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 the temperature 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