THERMO CHEMISTRY

Heating a substance in the same state requires energy in the for of Q=mcΔt

This uses masses of compounds

However, changing the state requires energy as well, in the form ΔH=nΔf/vHm

This uses moles of compounds

Fusion Melting and Boiling Condensation

Molar enthalpy of fusion of ice:

6.02kJ/mol =ΔfusHm

Meaning it takes 6.02kJ to melt 1 mole of ice at o oC into liquid water at 0 oC

Molar enthalpy of vaporization of water:

40.7kJ/mol = ΔvapHm

Meaning it requires 40.7kJ to turn 1mol of liquid water at 100oC to steam at 100oC

Use the chart on the previous page to answer the following questions:

1. Find the energy required to melt 255g of ice at 0 oC into water at 0

oC

2. Find the energy released when 36.0g of steam 100 oC condenses to water at 100 oC

3. Find the energy required to heat 250g of water from 25oC to 75oC.

4. Find the amount of heat absorbed by 355g of ice that goes from -87oC to -22oC

5. Water is considered to be a heat sink, find out how much energy is absorbed in the following samples and explain why.

a. 125g of water heats from 20oC to 80oC

b. 125g of Iron heats from 20oC to 80oC

6. How much energy is released when 150g of silver cools from 220oC to 80oC?

Challenge: If a 250g block of iron cools from 150oC to 60oC by putting it in 120g of water which ends up at 60oC. What was the initial temperature of the water?

7. Find the energy required to heat 125g of ice from -30.0 oC to water at 50.0 oC

8. Find the Energy released when 15g of steam at 150 oC condenses to water at 25 oC

9. Find the energy required to heat 1.5kg of ice at -50.0 oC to steam at 125 oC