Which of the following reactions could be classified as exothermic ?

1. Which of the following reactions could be classified as exothermic? • 2H2(g) + O2(g) 2H2O (g) + 241.8 kJ • reactants + energy products • N2(g) + O2(g) + 43kcal 2NO(g) • reactants products + energy ANSWER = A & D because… Any reaction that has energy on the products side is EXOTHERMIC! Any reaction that has energy on the reactants side is ENDOTHERMIC!

2. SPECIFIC HEAT B A • warm to touch • ice melts slower • higher specific heat • harder for energy to • move through • substance • cold to touch • ice melts faster • lower specific heat • energy moves through • substance easier

3. UNITS OF SPECIFIC HEAT Joules s = J g oC degrees Celsius grams Examples: Al = 0.89 J/goC and wood = 1.7 J/goC

4. 140 120 100 80 60 40 Temperature (oC) 20 0 -20 -40 -60 -80 -100 Time

5. An ice cube is heated from -65.0oC to -10.0oC. If the ice cube has a mass of 7.80g, how many Joules of energy were added to the system? (sice = 2.03 J/goC) Q = s ∙ m ∙ ∆T Q = (2.03 J/goC) (7.80g) (-10.0oC -(-65.0oC)) Q = 871 J

6. A werewolf hunter cools her newly handmade silver bullet from 952 oC to 22 oC in a bucket of water. Calculate the energy change in kcal for the bullet if it has a mass of 35.2 grams. Q = s ∙ m ∙ ∆T Q = (0.24 J/goC) (35.2g) (22oC - 952oC) Q = -7856.64 J

7. 100 80 71 70 58 60 50 50 40 40 26 26 21 21 20 20 16 10 10 5 3 0 1900 1940 1980 1990 2005 Wood Coal Petroleum / natural gas Hydro and nuclear Energy Sources in the United States 91 Percent 9 1850 Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 307

8. Energy Conversion fan electrical energy to mechanical energy coffee maker electrical energy to thermal energy light bulb electrical energy to light energy to thermal and radiant energy pencil sharpener electrical energy to mechanical energy Timberlake, Chemistry 7th Edition, page 202