Thermodynamics:

Measuring Energy in Chemical and Physical Changes

(Chapter 13 & 14)

Ch. 13/14 Overview

• What is Energy?• Why measure Energy?• Thermodynamic Concepts• The First Type of Energy Calculations

– Specific Heat– Heat of Fusion

What is Energy?

• Energy (q) is the ability to do work or supply heat

By Measuring Energy We Can…

• Understand Physical Changes– Why copper and aluminum pans heat faster than stainless steel– The temperatures at which a liquid will evaporate or freeze

• Harness the Power of Chemical Reactions– Thermochemistry

• Predict the Behavior of a Gas– The Gas Laws

• Find Ways to Do Useful Things– Make fuel efficient car engines– Create air conditioners

Thermodynamic Concepts

I. Enthalpy (H) is the total energy of a system

Enthalpy is a combination of the

– internal energy» Kinetic (energy of motion) - how fast all the matter is moving» Potential (stored energy)

» Chemical Bonds» Position or Arrangement of the Matter

– external energy» energy supplied to a system by its surroundings

» solids, liquids and gases can absorb or release energy from a difference in temperature (heat)

» or gases can absorb or release energy from work - changing pressure & volume

*total energy of a system cannot easily be measured, however changes in energy can – changes in energy are called “H”

II. A “System”

What is the System, and How is Energy Moving in and out?

What is the System, and How is Energy Moving in and out?

Thermodynamics and Heat

III. Thermodynamics = Measuring changes in Energy• It is difficult to measure every type of energy (H) in most

systems because there are so many ways that energy can be distributed.

• Scientists most often measure the transfer of energy between a system and its surroundings (H)

V. “Heat” is Energy Absorbed or Released because of a difference in temperature

• It is the amount of energy transferred between a system and it’s surroundings

The types of “Heat” we will measure…Temperature Changes (kinetic energy) Specific Heat

Melting or Freezing (phase change) Heat of Fusion Heat of Vaporization

Chemical Reactions (energy of chemical bonds) Heat of Reaction Heat of Combustion

Solids that Dissolve or Precipitate (energy of physical bonds) Heat of Solution

The “ΔH” is a measure of the energy change in a system

1. The amount of energy absorbed or released is always the same in both directions of a process - energy added is always equal to energy released

2. We can add individual inputs of energy together to determine the total amount of energy absorbed or released (Hess’s Law)

Lesson 13-1: Physical Change

Heat Capacitypg. 508-516

• Endothermic– Energy added

• Exothermic– Energy given off

• Heat Capacity– Amount of energy needed to raise temperature by 1°C

• Specific Heat (C) – Amount of energy needed to raise 1 g of a substance by 1°C

13-1: Specific Heat pg. 508-516

• Specific Heat (C)– Amount of energy needed to raise temperature of 1 g of a

material by 1°C

)()(

)(

CTgm

joulesqC

The equation can be rearranged to: q = m C ∆T

13-1: Specific Heat Conceptual Questions

Energy changes in an object are affected by both the mass and motion within the material

More mass = can absorb more energy

Motion of molecules = the freedom of molecules moving affects how energy is distributed: Vibration, Rotation and Translation

CONCEPT QUESTIONSWhich gets hot fastest on a sunny summer day?

• metal dog dish OR a metal dog dish full of water• Metal dog dish full of water OR a swimming pool

– How do your answers relate to mass and freedom of motion of molecules?

Homework

• 13-1 Lesson Questions

• Heat and Its Measurement WS

Working Classroom Examples

• Ex. 1 pg. 510• Ex. 2 pg. 512• Ex. 3 pg. 514

• WS #3