Catalyst

End

100 oC Water Burn 100 oC Steam Burn

Justify – TPS• Why is it worse to be burnt by 100 oC steam

than 100 oC water? Justify your answer with Word Wall vocab!

Lecture 7.4 – Latent Heats

Today’s Learning Target• 7.7 – I can use the latent heat of phase change

to calculate the amount of energy that is released or absorbed during a change of phase.

What are Latent Heats?

I. ΔHfusion and ΔHvaporization

• There is energy required to change phases• ΔHfusion = Energy to change solid to a liquid.

• ΔHvaporization = Energy to change liquid to a gas.

• ΔHfreezing = Energy to change liquid to a solid

• ΔHcondensation = Energy to change gas to a liquid

II. Latent Heat• Can calculate the amount of energy needed to

convert a substance from one phase to another• Latent Heat – The energy absorbed as a

substance changes phases

ΔH of vaporization/condensation

ΔH of fusion/freezing

Latent Heats

How do you calculate latent heats?

I. Equation for Latent Heat

• m = mass of compound• ΔH = Enthalpy values for phase changes

(constants)• Easy way to remember: Q equals maH! (The delta

kinda looks like an A!)

Class Example

• You have a 2000 kg of ethanol. Calculate the energy you would need to turn solid aluminum into liquid. The ΔHfusion is 109 kJ/kg.

Table Talk• You have 6342 kg of mercury. How much energy

would be required to take mercury from liquid to a gas? The ΔHvaporization is 294 kJ/kg

Stop and Jot

• You have an ice cube of H2O that weighs 2000 kg and you melt it to liquid. How much energy does that require? The ΔHfusion is 334 kJ/kg.

SUMMARIZE

Checklist Manifesto!• How do I know which equation to use?Does it have specific heat?

Then use calorimetry!Does it give you ΔH or ΔT

If ΔH then use q = mΔHIf ΔT then use q = m x Cp x ΔT

Box the one it’s asking you to find!Plug in the right numbers and solve!

Connect 4

• Begin working on your “Homework 7.3”• There will be an exit slip after this activity

Work Time

Learning Log AssessmentRate yourself 1 – 4 on LTs 7.1-7.7

1. You have 2000 g of water that is heated from 25 C to 100 C. What is the heat absorbed by this process. The specific heat of water is 4.184 J/(gxC)

Exit Slip

Learning Log AssessmentRate yourself 1 – 4 on LTs 7.7

• Test Thursday/Friday!

Closing Time