Chapter 10 Energy 10.1 The Nature of Energy Energy- the ability to do work or produce heat Potential energy- energy due to position or composition Kinetic energy- energy due to motion of the object; determined by mass & velocity Law of Conservation of Energy- energy can be converted from one form to another but can neither be created nor destroyed Work- force acting over a distance (W = F x d) State Function- property of a system that changes independently of its pathway

10.2 Temperature & Heat Temperature- measure of the random motions of the components of a substance Heat- flow of energy due to temperature difference Temperature is measured in degrees Celsius in lab; the metric system unit for temperature is Kelvin. Heat is measured in calories; 1 calorie is the amount of heat necessary to heat 1 gram of water by 1 degree Celsius. The metric system unit for heat is Joules. 1 calorie = J

Figure 10.2: Equal masses of hot and cold water.

Figure 10.3: H 2 O molecules in hot and cold water.

Figure 10.4: H 2 O molecules in same temperature water.

10.3 Exothermic & Endothermic Processes System- part of the universe on which we wish to focus attention Surroundings- everything else in the universe (see next slide) *Exothermic- heat is evolved; heat exits *Endothermic- process that absorb energy from the surroundings The energy gained by the surroundings must be equal to the energy lost by the system.

Figure 10.5: The energy changes accompanying the burning of a match.

10.4 Thermodynamics Thermodynamics- study of energy 1 st Law of Thermodynamics- the energy of the universe is constant. E- internal energy; sum of kinetic and potential energies of all particles in the system. /\E = q + w q is heat w is work Sample problem:

10.5 Measuring Energy Changes Units of Heat Calorie- amount of energy needed to raise the temperature of 1 gram of water by one degree Celsius (or 1 Kelvin) Joule- metric system unit of heat; 1 calorie = joule It takes joules to raise the temperature of 1 gram of water by 1 degree Celsius Example 10.1, p. 295: Express 60.1 cal in joules? Problem 10.1, p. 295: How many calories of energy correspond to 28.4 J?

Specific heat capacity- amount of energy required to change the temperature of 1 gram of a substance by 1 degree Celsius Water: specific heat = 1 cal/g o C or J/g o C q = mc/\T(/\T = T final – T initial )

Figure 10.6: A coffee-cup calorimeter.

Problem 10.2, p. 296: Calculate joules required to heat 454 grams of water from 5.4 o C to 98.6 o C. Note Table 10.1, p. 297 Problem 10.3, p. 299: A 5.63 gram sample of solid gold is heated from 21 o C to 32 o C. How much energy (in joules and in calories) is required?

Problem 10.4, p. 300: A 2.8 gram sample of pure metal requires 10.1 J of heat to change its temperature from 21 o C to 36 o C. What is this metal? (Use Table 10.1)

10.6 Thermochemistry (Enthalpy) Enthalpy- heat that is produced or absorbed in a reaction. For most reactions, /\H p = heat Problem 10.5, p. 302: The reaction that occurs in heat packs used for sports injuries is 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s) /\H = kJ How much heat is released when 1.00 gram of iron is reacted with excess oxygen gas?

10.7 Hess’s Law The change in enthalpy is the same whether the reaction takes place in one step or in a series of steps. 1.If a reaction is reversed, the sign of /\H is changed. 2.The magnitude of /\H is directly proportional to the quantities of reactants and products

10.8 Quality v. Quantity of Energy 10.9 Energy and Our World (read carefully; questions on the test)

Figure 10.7: Energy sources used in the United States.

Figure 10.8: The earth’s atmosphere.

Figure 10.9: The atmospheric CO 2 concentration over the past 1000 years.

10.10 Energy as a Driving Force Energy spread- concentrated energy is dispersed widely Matter spread- molecules are spread out and occupy a larger volume Entropy (S) = chaos The entropy of the universe is increasing. (2 nd Law of Thermodynamics) Example: (NH 4 ) 2 CO 3 (s)  2NH 3 (g) + H 2 O(g) + CO 2 (g) H 2 O(s)  H 2 O(l)  H 2 O(g)

Figure 10.10: Comparing the entropies of ice and steam.