1. Energy Solving Quantitative Energy Problems

2. Energy Transfer
When a system absorbs energy from the surroundings, there is an increase in:
Thermal Energy (temperature goes up), OR
Phase Energy (goes to a more energetic phase)
Surroundings
System

3. Energy Transfer
When a system releases energy from the surroundings, there is a decrease in:
Thermal Energy (temperature goes down), OR
Phase Energy (goes to a less energetic phase)
Surroundings
System

4. What info do we need to know how much thermal energy is transferred between a system and the surrounding?
The amount of thermal energy transferred depends on:
The change in temperature
The amount of sample 80
Temp (°C) 25
Time / Energy Added

5. Think of our Metal Vs. Wood example: Does it take the same amount of energy to raise the temperature 1°C for both 1 g of wood and 1 g of metal?
No; Because the metal is better at transferring energy than the wood.
It takes less energy to raise the temperature of 1 g of metal 1°C than it does to raise the temperature of 1 g of wood 1°C.

6. Specific Heat Capacity (Specific Heat or Heat Capacity)
Specific Heat Capacity (c) – the amount of energy required to raise the temperature of 1 gram of a substance 1°C.
It is specific for the substance. Each substance has a different specific heat.
Example: the specific heat of liquid water is:
*Do NOT memorize these values; specific heats will always be given

7. A cup of coffee (120 g), which is mostly water cools from 95˚C down to 10.˚C. How much energy does it release to the surroundings?
Given:
c = 4.18 J/g ˚C
m = 120g
ΔT = 85˚C
Find: Q

8. What info do we need to figure out how much phase energy is transferred between a system and the surrounding?
100
100
Temp (°C)
Temp (°C)
Time / Energy Added
Time / Energy Added
The amount of phase energy transferred depends on:
The amount of sample only.

9. Latent Heat
Latent Heat – the amount of energy absorbed or released by a system during a process that occurs when there is no temp change (ex. Phase change).
Latent Heat is specific to the substance and the phase change.
Latent Heat of Fusion (Hf) – melting or freezing
Latent Heat of Vaporization (Hv) - evaporating or condensing

10. Latent Heat of Water
Heat of Fusion (Hf) Heat of Vaporization (Hv)
How would you expect the Heat of Vaporization of water to compare the Heat of Fusion?

11. Suppose during volleyball practice, you lost 845 g of water due to sweating. If all of this water evaporated, how much energy did the water absorb from your body? Express your answer in kJ.
Given:
Hv = 2260 J/g
m = 845 g
Find: Q

12. Suppose during volleyball practice, you lost 1
Suppose during volleyball practice, you lost 1.40 lbs of water due to sweating. If all of this water evaporated, how much energy did the water absorb from your body? Express your answer in kJ lbs = 1.0 kg
Given:
Hv = 2260 J/g
m = 1.40 lbs
Find: Q