1. Warm up 1-22-15 1.In an exothermic reaction, the products have (more/less/same) energy as the reactants? 2.Positive enthalpy is a _______ reaction 3.Adding 234 J to 5g of a substance and the temperature increased by 35 K, what is the specific heat? Agenda -Fireproof balloon? -Notes Unit 6-4 -WS 6-4 problems Homework Jan 29 – Online HW

2. Fireproof Balloon Add water in your balloon and apply heat to the balloon from the candle Add air to your balloon and apply heat from candle

3. Unit 6-4 Latent Heat

4. Latent Heat Latent heat is when a substance changes phase (liquid, solid, gas) During the phase change, heat is absorbed or released but temperature doesn’t change

5. Latent Heat Latent heat of fusion – (ΔH fus ) the total energy required to melt 1 gram of a substance Latent heat of vaporization – (ΔH vap ) - the total energy required to evaporate 1 gram of a substance

6. Latent Heat Graph ΔH fus ΔH vap 0oC0oC 100 o C

7. Latent Heat Equations Heat required to melt a substance Q = (ΔH fus ) (mass) Ice melting ΔH fus = 334 J/g Heat required to evaporate a substance Q = (ΔH vap ) (mass) Water boiling ΔH vap = 2260 J/g

8. Practice Problem #1 ΔH fus Ice melting = 334 J/g ΔH vap Water boiling= 2260 J/g Determine the amount of heat for 80 grams of water to completely evaporate.

9. Practice Problem #2 ΔH fus Ice melting = 334 J/g ΔH vap Water boiling= 2260 J/g Determine the number of grams of ice that can be melted by 0.800 kJ of heat.

10. Practice Problem #3 ΔH fus Ice melting = 334 J/g ΔH vap Water boiling= 2260 J/g Cp of water vapor = 1.89 J/g·C Cp of water liquid = 4.18 J/g·C Cp of water ice = 2.05 J/g·C How much heat is required to bring 23 grams of water at 80ºC to 110 ºC?

11. Practice Problem #4 ΔH fus Ice melting = 334 J/g ΔH vap Water boiling= 2260 J/g Cp of water vapor = 1.89 J/g·C Cp of water liquid = 4.18 J/g·C Cp of water ice = 2.05 J/g·C How much energy is needed to convert 175 grams of water from -8˚C to 26˚C

12. Assignments Summary Turn in Virtual Lab Calorimeter WS 6-3 Practice Problems

13. How to light a candle without touching the flame to the wick?