1. Warm Up #2
In an endothermic reaction, if 350 J of heat is absorbed, how much heat is lost by the surroundings? How do you know?
If the final temperature of 56.0 g of water was 95oC after 350 J of heat were added, find what the initial temperature of water is, given water’s specific heat of 4.18 J/(oC•g)
Draw a diagram for an exothermic reaction. Show on this diagram how a catalyst would affect the reaction. Explain this in words.
Is melting considered an endothermic or an exothermic process? What about condensation? How do you know?

2. Chapters
Measuring Heat

3. Review
Heat (q) – TRANSFERRED from system to surroundings and vice versa (joules or calories)
qsystem = -qsurroundings
Endothermic vs. Exothermic
Measuring Heat: q = m • c • ΔT
C = specific heat – amt of energy it takes to raise 1 g of a substance up 1oC
1 kilojoule (kJ) = 1000 joules 1 kilocalorie = 1000 calories

4. ΔH and q
ΔH = enthalpy – the heat content of a system at constant pressure
ΔH = qsystem
For endothermic reactions (melting): ΔH = positive
For exothermic reactions (freezing) : ΔH = negative
ΔH = kJ/mol

5. Measuring ΔH in Phase Changes
Phase changes – going from one phase to another
NO TEMP CHANGE, just heat added/taken away
Liquid to solid = freezing (exo)
Solid to liquid = melting (endo)
Gas to liquid = condensation (exo)
Liquid to gas = vaporization (endo)

6. Liquid Solid Phase Change
ΔHfus = molar heat of fusion – amt of energy needed to melt 1 mol of solid substance (kJ/mol)
For H2O: ΔHfus = 6.01 kJ/mol (endo)
ΔHsolid = molar heat of solidification – opposite of fusion
ΔHsolid for H2O = kJ/mol (exo)

7. Liquid  Gas Phase Change
ΔHvap = molar heat of vaporization – amt of energy needed to boil 1 mol of liquid substance (kJ/mol)
For H2O: ΔHvap = 40.7 kJ/mol (endo)
ΔHcond = molar heat of condensation– opposite of vaporization
ΔHcond for H2O = kJ/mol (exo)

8. Quick Quiz #2
Is vaporization an endothermic or an exothermic process? How do you know? How will that affect the energy in the system?
How much energy is generated, in kilojoules, when you boil grams of water? (ΔHvap = 40.7 kJ/mol )
If the molar heat of solidification of water is KJ/mol, how much water, in grams, was frozen if 109 KJ of energy was released.