Unit 1 ENERGY1.1 How do you read a heating

and cooling curve?March 22, 2010

Objective: SWBAT identify the parts of a heating

curve and a cooling curve

DO NOW:

Heat of Reaction

(ΔH) = HProducts - HReactants

(ΔH) = D - A

Let’s think of something heating up…

1. What happens to its temperature?

2. What happens to particles of the substance?

It increases because HEAT IS ADDED

Particles start to spread out

HEATING CURVE

Let’s study the graph

1. What phase changes do you notice on the graph?

Solid turning to liquid Melting

Liquid turning to gas Boiling

MELTING• This is also known as fusion.

• During the melting process, the temperature remains constant even though heat is still being added at a constant rate.

• Both solid and liquid phases of the substance are present during the melting process.

• As time goes on, the amount of liquid continually increases and the amount of solid continually decreases. The amount of heat needed to convert a solid at its melting point to a liquid is called the heat of fusion.

And then…

When the entire solid has melted and only the liquid phase is present, the temperature once again begins to rise. The temperature continues to rise until the boiling point is reached.

BOILING• This is also known as vaporization.

• Once boiling begins, the temperature remains constant as the energy increases.

• During this phase change, both the liquid and gaseous (vapor) phases are present.

• The amount of heat needed to convert a liquid at its boiling point to a gas is called the heat of vaporization.

COOLING CURVE

Task: After learning how a heating curve works, construct a cooling curve with a partner.

Label the parts:FreezingCondensing

Let’s Review

What is reverse of boiling?

What is reverse of melting?

condensation

freezing Also known as SOLIDIFICATION

SUBLIMATION AND DEPOSITION

Some substances change directly from a solid to a gas without passing through a

liquid phase.

The process, in which a solid changes directly into a gas, is called sublimation.

The reverse of sublimation, in which a gas changes directly into a solid, is called

deposition.

Let’s Try Some1. The temperature of a sample of a substance is increased from 20.°C to 160.°C as the sample absorbs heat at a constant rate of 15 kilojoules per minute at standard pressure. The graph below represents the relationship between

temperature and time as the sample is heated.

a) What is the boiling point of this sample?

b) What is the total time this sample is in the liquid phase, only?

c) What is the melting point of this sample?

d) What is the range of temperature at which the sample is in the gas phase, only?

Between 4 minutes and 7 minutes. 7- 4 = 3 minutes

120oC

70oC

120oC- 160oC

2. The graph below shows a compound being cooled at a constant rate starting in the liquid phase at 75°C and ending at 15°C.

a) What is the freezing point of the compound, in degrees Celsius?

b) State what is happening to the average kinetic energy of the particles of the sample between minute 2 and minute 6.

c) A different experiment was conducted with another sample of the same compound starting in the solid phase. The sample was heated at a constant rate from 15°C to 75°C. Draw the resulting heating curve.

d) What Kelvin temperature is equal to 15°C?

50oC

(Kinetic=motion) since temperature decreases, Kinetic energy also decreases

273K = 0oC

So 15oC = ?K

273 + 15 = 288K

INDEPENENT PRACTICE

COMPLETE FOR HOMEWORK IF YOU ARE NOT DONE IN CLASS.

ASSIGNMENT IS TO BE COMPLETED BY TOMORROW!!!