1. Warm-up Mg(s) + HCl(aq)  H 2 (g) + MgCl 2 (aq) How much H 2 (g) is produced (in grams) in the above reaction if we have a mass of 0.9 grams Mg and 1.87 grams of HCl? Mg = 24.31g/mol H = 1.01g/mol Cl = 35.45g/mol

2. Objective SWBAT calculate energy changes in a thermodynamics problem set

3. Chemical Thermodynamics Standard 7

4. Specific Heat 7d The specific heat of a substance is the amount of energy needed to change the temperature of 1gram by 1˚C. ◦ Every substance has its own specific heat. Specific Heats of Common Substances SubstanceSpecific Heat (J/g˚C) Water (l)4.184 Ethanol (l)2.44 Aluminum (s)0.897 Silver (s)0.235 Gold (s)0.129

5. Logical Thinking (don’t write) Since it takes 4.184 Joules to raise the temp of 1gram of water 1˚C, how much would it take to: ◦ Raise 2 grams 1˚C? ◦ Raise 1 gram 2˚C? ◦ Raise 2 grams 2˚C?

6. Heat added here doesn’t change the temperature of the substance, it is causing the phase change.

7. Heat Flow Problems To calculate heat, use the following formula: ◦ Energy = mass * specific heat * temperature change Always given to you!

8. Practice Problems If 200.0 grams of water is heated from 70.0° C to 100.0° C to make a cup of tea, how much heat must be added? Q = (m)(c)( ΔT) Joules Calculations: 4.184J/gC

9. Latent Heat7d cont Latent (hidden) heat is energy added to a substance that doesn’t change the temperature. ◦ Instead, it is used to change the phase solid  liquidliquid  gas What is latent heat and what is it used for?

11. Energy Requirements for the Changes of State Changes of state are physical changes ◦ No chemical bonds are broken

12. Energy Requirements for the Changes of State Molar heat of fusion – energy required to melt 1 mol of a substance Molar heat of vaporization – energy required to change 1 mol of a liquid to its vapor

13. Practice Problems If 200.0 grams of water is at 100.0° C, how much heat must be added to change it all to steam or gas? H vap = 40.6 kj/mol Calculations:

14. Putting it all together If 200.0 grams of water is heated from 70° C to 100.0° C and then a complete phase change is made to steam, how much energy was required? Calculations:

15. Summary What is temperature What happens when you heat a substance? Describe endo/exothermic reactions. What is ΔH for endo/exothermic reactions? Where does the energy go during phase changes? Be able to calculate heat problems. What is latent heat used for?