Download Section 10.2 The Flow of Energy

Section 10.2
The Flow of Energy
Objectives
1. To understand how energy flow affects internal energy
• How much energy is there in a substance?
2. To understand how heat is measured
• What are the units of energy?
3. To understand how the flow of heat changes temperature
• How does an amount of heat gained or lost relate to a
change in temperature?
Section 10.2
The Flow of Energy
A. Thermodynamics
• Thermodynamics – the study of energy
• First law of thermodynamics
– Energy of the universe is constant
or
– Energy can neither be created nor
destroyed
Where does the energy come from and
go to in a basketball game?
Section 10.2
The Flow of Energy
A. Thermodynamics
• Internal Energy, E – sum of kinetic and potential
energies of all the “particles” in a system
– Internal energy can be changed by two types of
energy flow:
• Heat (q)
• Work (w) – a force acting over a distance
E = q + w
I can warm a beaker of water with my hands or I can
push it across the bench – which is q and which is w?
Section 10.2
The Flow of Energy
A. Thermodynamics
• Thermodynamic quantities always consist of 3 parts:
– A number (magnitude of the change)
– A unit of energy
– A sign (indicates the direction of flow in or out of
the system)
ΔE = -145kJ
Heat is given off - exothermic
ΔE = + 377kJ
Heat is absorbed - endothermic
Section 10.2
The Flow of Energy
Section 10.2
The Flow of Energy
B. Measuring Energy Changes
• The common energy units for heat are the calorie and the
joule.
– calorie : the amount of energy (heat) required to raise
the temperature of one gram of water by 1oC.
– Joule : 1 calorie = 4.184 joules
How many Joules does it take to
raise the temperature of 1 gram of
water by 1oC?
1000 calories = 1kcal = 1 Calorie
Section 10.2
The Flow of Energy
B. Measuring Energy Changes
Section 10.2
The Flow of Energy
B. Measuring Energy Changes
• Specific heat capacity is the
energy required to change
the temperature of a mass of
one gram of a substance by
one Celsius degree.
High Specific Heat Capacity of Water
Section 10.2
The Flow of Energy
B. Measuring Energy Changes
• To calculate the energy required to raise the temperature of
a substance:
Q = s x m x t