1. 11.3 Heat in Changes of State

2. Warm up Is it exo- or endo- thermic???? -negative ΔH -positive ΔH -Heat as a reactant -Heat as a product -Combustion of fossil fuels

3. Heat, Q or Δ H, has been discussed so far to describe an amount of heat absorbed or released for a substance in a single state. Q = mcΔT

4. Phase Changes

5. Solid  Liquid  Gas – Requires an addition of heat into the system – Endothermic Processes Gas  Liquid  Solid – Heat leaves the system – Exothermic Processes

6. Phase Changes Melting / Solidification – ΔH fusion Vaporization / Condensation – ΔH vaporization

7. Problem Solving for a Phase Change For Solid to Liquid or Liquid to Solid USE ΔH fusion For Liquid to Vapor or Vapor to Liquid USE ΔH vaporization

8. How many grams of ice at 0  C can be melted by the addition of 5 kJ of heat? For water Δh fus = 6.01 kJ/mol

9. How many grams of ice at 0C can be melted by the addition of 5 kJ of heat? For water Δh fus = 6.01 kJ/mol First we can solve for moles 5 kJ 1 mol = 0.83 mol 6.01 kJ Are we done??? 0.83 mol 18 g = 14.94 g mol

10. How much heat is absorbed when 50 g of 100 °C liquid water is converted to steam at 100 °C ? ΔH vap = 40.7 kJ /mol How do you think you might start this problem???

11. How much heat is absorbed when 50 g of 100 °C liquid water is converted to steam at 100 °C ? ΔH vap = 40.7 kJ /mol 50 g 1 mol 40.7 kJ = 113.05 kJ 18 g mol

12. Calculating heat change using Q = mΔH Instead of being given ΔH as a kJ/mol value, you may be given a J or cal per gram unit….. ΔH fusion for water is 334 J/g ΔH vaporization for water is 2260 J/g Then you can just plug and chug!!!!

13. How much heat is released when 2 grams of liquid water at 0°C turns to ice at 0°C? Q = mΔH ΔH fusion for water is 334 J/g

14. How much heat is released when 2 grams of liquid water at 0°C turns to ice at 0°C? Q = mΔH ΔH fusion for water is 334 J/g Q = ( 2 g )(334 J/g) = 668 J

15. Solving for heat when both a temperature change and phase change occur….. Q = mcΔT + mΔH

16. Let’s practice… How much heat is required to convert 20 g of water at 28°C into steam at 100°C ? Specific heat of water = 1 cal/g°C ΔH vaporization = 540 cal/g Q = mcΔT + mΔH

17. Let’s practice… How much heat is required to convert 20 g of water at 28°C into steam at 100°C ? Specific heat of water = 1 cal/g°C ΔH vaporization = 540 cal/g Q = mcΔT + mΔH Q = (20 g)(1 cal/g°C)(72 °C) + (20g)(540 cal/g) Q = 12240 cal

18. In class: Ch. 11 Practice Problems Ch. 11.2 Quiz on Friday!!!