1. Chapter 10 Energy Chemistry 101

2. Energy MatterEnergyEmpty space Universe Energy: ability to do work or produce heat.

3. Energy Kinetic energy (KE): energy of motion KE = ½ mV 2 V: velocity Potential energy (PE): stored energy Law of conservation of energy (Position & Composition)

4. Kinetic and Potential Energy A B B A Kinetic energy Potential energy Change in potential energy for ball A (change in level) Work: change the position of ball B Heat: friction between surface & ball Frictional heating (heat is a form of energy). T of hill increases

5. Heat and Temperature Temperature: measure of random motions of the components of substance. T ↑ move faster Kinetic energy ↑

6. Energy is transferred from high T to low T. Heat: Flow of energy due to a T difference. Heat and Temperature Cold Water Hot Water T final = T hot initial + T cold initial 2 T final

7. Heat units of heat: calorie (cal) English system joule (J) SI system 1 cal = 4.184 J Joule: Energy (heat) required to raise T of one gram of water by 1  C. Food energy is measured in Calories (note the capital C). 1 Cal = 1 kcal = 1000 cal

8. Amount of heat = specific heat × mass × change in temperature Amount of heat = SH × m × (T 2 – T 1 ) T 2 = final temperature T 1 = initial temperature SH = Specific heat capacity (cal/g °C) m = mass (g) Heat

9. Note: ALEKS uses “c” instead of “SH” to stand for specific heat capacity. Specific heat capacity is the energy required to change the temperature of a mass of one gram of a substance by one Celsius degree. Heat

10. Calculate the amount of heat energy (in joules) needed to raise the temperature of 6.25 g of water from 21.0°C to 39.0°C. We are told the mass of water and the temperature increase. We look up the specific heat capacity of water, 4.184 J/g°C. Q = SH x m x  T Q = (4.184 J/g°C) x (6.25 g) x (39.0°C – 21.0°C) Q = 471 J Practice 1: Heat

11. A silver-gray metal weighing 15.0 g requires 133.5 J to raise the temperature by 10.°C. Find the heat capacity. Q = SH x m x  T (133.5 J) = SH x (15.0 g) x (10.°C) SH = 0.89 J/g°C Can you determine the identity of the metal using Table 10.1? Heat Practice 2: Al

12. Heat of reaction C 3 H 8 (s) + 5O 2 (g)  3CO 2 (g)+ 4H 2 O(l) + heat (energy) 2HgO(s) + heat (energy)  2Hg(l) + O 2 (g) Endothermic reaction Exothermic reaction All combustion reactions are exothermic.

13. Heat of reaction Surroundings System Energy Exothermic Endothermic  (PE) Reactant Product Energy released to the surroundings as heat Surrounding Exothermic (burning) Exothermic = exit!

14. Classify each process as exothermic or endothermic. Explain why. (The system is underlined.) a)Your hand gets cold when you touch ice. b)The ice gets warmer when you touch it. c)Water boils in a stove-top kettle. d)Water becomes ice in the freezer. e)Water vapor condenses on a cold pipe. f)Ice cream melts. Exo Endo Exo Endo Heat of reaction Practice:

15. Thermodynamics Thermodynamics: study of energy Internal energy (E): sum of the kinetic and potential energies.  E = q + w  “delta”: change Work Heat Law of conservation of energy: energy of the universe is constant. The first law of thermodynamics:

16. Surroundings System Energy Exothermic Endothermic  E  0  E  0 Thermodynamics  E = q + w Energy flows into system via heat (endothermic): q = +x Energy flows out of system via heat (exothermic): q = -x System does work on surroundings: w = -x Surroundings do work on the system: w = +x

17. Enthalpy For a reaction in constant pressure, the change of enthalpy is equal to energy that flows as heat.  H p = heat Constant pressure “-” heat or  H p : exothermic: heat flows out of the system. “+” heat or  H p : endothermic: heat flows into the system. Enthalpy (Thermochemistry): heat of chemical reactions.

18. Calorimetry Calorimeter: A device to measure the heat energy released or absorbed by a reaction.  T   H

19. S(s) + O 2 (g)  SO 2 (g) ΔH = –296 kJ Calculate the quantity of heat released when 2.10 g of sulfur is burned in oxygen at constant pressure. Use the  H value like a conversion factor. 2.10 g S = 0.0655 mol S x 1 mol S 32.26 g S 0.0655 mol S = – 19.4 kJ x – 296 kJ 1 mol S Enthalpy Practice:

20. Hess’s Law State function: a property of system that changes independently of its pathways. Enthalpy is a state function. In a chemical reaction, change of enthalpy is the same whether the reaction takes place in one step or in a series of steps. N 2 (g) + 2O 2 (g)  2NO 2 (g)  H 1 = 68 kJ 1 Step N 2 (g) + O 2 (g)  2NO(g)  H 2 = 180 kJ 2NO(g) + O 2 (g)  2NO 2 (g)  H 3 = -112 kJ N 2 (g) + 2O 2 (g)  2NO 2 (g)  H 2 +  H 3 = 68 kJ 2 Steps

21. Two rules about enthalpy 1. If a reaction is reversed, the sign of  H is also reversed. N 2 (g) + 2O 2 (g)  2NO 2 (g)  H 1 = 68 kJ 2NO 2 (g)  N 2 (g) + 2O 2 (g)  H 1 = -68 kJ 2. If the coefficients in a balanced reaction are multiplied by an integer, the value of  H is also multiplied by the same integer. N 2 (g) + 2O 2 (g)  2NO 2 (g)  H 1 = 68 kJ 2N 2 (g) + 4O 2 (g)  4NO 2 (g)  H 1 = 2  68 kJ = 136 kJ  2

22. Law of conservation of energy Quality-Quantity of Energy Why are we concerned about energy? Gasoline + O 2  CO 2 + H 2 O + energy Spread in universe Concentrated energy Spread energy Use of energy to do work Quantity Quality Heat death

23. Energy and Our World Sun Woody plants Coal Natural gas Petroleum Photosynthesis Source of energy 6CO 2 + 6H 2 O + energy of sun C 6 H 12 O 6 + 6O 2 Photosynthesis glucose

24. 1. Natural gas –90 to 95 percent methane. –5 to 10 percent ethane, and a mixture of other low-boiling alkanes. 2. Petroleum –A thick liquid mixture of thousands of compounds, most of them hydrocarbons. Energy and Our World Fossil Fuels: formed from the decomposition of marine plants and animals. (C 5 -C 10 ) (C 10 -C 18 ) (C 1 -C 4 ) (C 15 -C 25 ) (  C 25 )

25. 3. Coal –Was formed from the remains of plants that were buried (under high P and T). –20% of our energy. –Expensive, dangerous, and produces pollution (CO & SO 2 ). Energy and Our World

26. Greenhouse Effect

27. Driving forces Energy spread: concentrated energy is dispersed widely. (Exothermic process) Matter spread: molecules of a substance are spread out and occupy a larger volume. Dissolving is endothermic process, but because of matter spread, it occurs. heat

28. Entropy (S) A measure of disorder or randomness. Energy spread  Faster random motions of the molecules in surroundings. Matter spread  Components of matter are dispersed (occupy a larger volume). A Spontaneous process is one that happens in nature on its own. (because of increasing entropy) Dissolving The second law of thermodynamics: The entropy (S) of the universe is always increasing. We run towards a disorder (heat death of universe).

29. Midterm 2 Bring a 2B pencil. One 30423 Scantron form (available in Runner Bookstore). A calculator (scientific, not graphing).