Unit 8 Energy

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liquid
water

ice&water

water&
steam

ice

steam

The first horizontal line is the constant temperature for change of solid to liquid. This the the melting point e.g. mp water = 0^oC

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24

Heating/Cooling Curve

HEAT – measure of the amount of energy transferred from one substance to another

- measured in units of joules (SI unit) or calories
- 4.184 J = 1 calorie

Calorimeter - device used to measure heat

How do we calculate heat?

specific heat ( C ) - amount of heat energy required to raise the temperature of 1 g of material 1C (or 1 K )

Heat of Vaporization ( Hv) - amount of energy
needed to vaporize 1 g of a liquid at its boiling point

Hv for water = 2260 J/g

Heat of Fusion ( Hf) - amount of energy needed to melt 1 g of a solid at its melting point

Hf for water = 334 J/g

Problem 1: How many joules are required to
vaporize 1000g of water?

q= 1000 g X 2260 J = 2260000 J = 2.26 X 106 J
g

Problem 2: If we melted 70 g of ice to water, how
much energy would the ice need to absorb?

melting or freezing is
heat of fusion

Q = 70 g X 334 J = 23,380 J
g

Some text here about the topic of discussion

Answer the following questions using the chart above.

1. What is the freezing point of the substance?

2. What is the
boiling point of the
substance?

3. What is the
melting point
of the substance?

B

B

D

4. What letter represents the range
where the solid is being warmed?
A
5. What letter represents
the range where the
liquid is being warmed?
C
6. What letter represents
the range where the
vapor is being warmed?
E
7. What letter represents
the melting of the solid?
B

8. What letter represents the
vaporization of the liquid?
D
9. What letter(s) shows a
change in potential energy?
B and D
10. What letters(s) shows a
change in kinetic energy?
A, C, and E