1. Energy & Chemical Change Chapter 16

2. 16.1 ENERGY Energy = the ability to do work or produce heat. –Kinetic energy is energy of motion. –Potential energy is stored energy.

3. Potential(highest) loosing potential gaining kinetic Kinetic (highest)

4. Chemical systems (like a roller coaster or pendulum) contain both kinetic and potential energy.

5. 16.1 Law of conservation of energy = in any chemical reaction or physical process, energy can be converted from one form to another, but is neither created nor destroyed.

6. Potential to electric

7. Chem potential to heat

8. 16.1 Chemical potential energy = energy stored in a substance because of its composition. Octane (C 8 H 18 ), a major component of gasoline, stores potential energy in its hydrogen – carbon bonds. -C-C-C-C-C-C-C-C-

9. As it oxidizes, the potential energy changes to kinetic energy that moves the pistons, and also to heat. C 8 H 18 + O 2  CO 2 + H 2 O + energy(heat)

10. 16.1 Measuring heat Heat = (q) energy that is in the process of flowing from a warmer object to a cooler object. calorie= amount of heat required to raise the temperature of one gram of pure water by one degree Celsius. Nutritionally, a Calorie (capitalized) = 1000 calories.

11. 16.1 Joule (j)= SI unit of heat and energy. Conversion factors page 491: 1 cal = 4.184 j 1 kj = 1000 joules 1 Calorie = 1 kilocalories = 1000 cal

12. From 16.1 q = c x m x ∆T q = heat absorbed or released c = specific heat of substance (table 16-2) m = mass ∆ T = temperature change

13. P 495 problem 4 If the temperature of 34.4 g of ethanol increases from 25.0°C to 78.8°C, how much heat has been absorbed by the ethanol? q = c x m x ∆T q = 2.44 J/g°C x 34.4 g x 53.8°C q = 4,520 J

14. 16.2 Calorimeter = an insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process

15. Determining specific heat Use the calorimeter to determine the specific heat of an unknown metal. 1. Put a known amount of water into a styrofoam cup and find initial temperature. m = 125 g 2.Heat the metal to a known temperature and then place it in the water. T metal = 115°C

16. 3. Place metal into water until temperature stabilizes. T = 29.3°C 4. Calculate the heat gained by the water. q = c x m x ∆T q water = 4.184 J/g°C x 125 g x (29.3°C - 25.6°C) q water = 1900 J

17. 5.Assume that the water gains the same amount of heat that the metal loses. q metal = c x m x ∆T 1900 J = c metal 50.0g x 85.7°C 1900 J = c metal 50.0g x 85.7°C c metal =.44 J/g°C

18. System = reaction or process being studied Surroundings = everything other than the system Universe = system + surroundings

19. Enthalpy (H) = the heat content of a system at constant pressure. ∆H rxn = ∆H products - ∆H reactants When reactants have more energy than products, ∆H rxn is negative. This means the system loses energy, is exothermic.

20. ∆H rxn = ∆H products - ∆H reactants When products have more energy than reactants, ∆H rxn is positive. This means the system gains energy, is endothermic.

21. 16.3 Thermochemical equation = a balanced chemical equation that includes the physical states of all reactants and products and the enthalpy change (∆H).

22. 4 Fe (s) + 3O 2 (g)  2Fe 2 O 3 (s) + 1625 kJ 4 Fe (s) + 3O 2 (g)  2Fe 2 O 3 (s) ∆H=-1625 kJ The negative value for ∆H means that the system (reaction) is losing energy, giving off heat, is exothermic.

24. 27 kJ + NH 4 NO 3 (s)  NH 4 + (aq) + NO 3 - (aq) NH 4 NO 3 (s)  NH 4 + (aq) + NO 3 - (aq) ∆H = 27 kJ The positive value for ∆H means that the system (reaction) is gaining energy, taking in heat, is endothermic.

26. PreAP also must know sections 3-5, unfortunately, nothing exists on powerpoint at this time on these sections…