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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
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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 = 4.184 J
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 1st 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 = 4.184 joule It takes 4.184 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 oC or 4.184 J/g oC q = mc/\T (/\T = Tfinal – Tinitial)
Problem 10.2, p. 296: Calculate joules required to heat 454 grams of water from 5.4oC to 98.6oC. Note Table 10.1, p. 297 Problem 10.3, p. 299: A 5.63 gram sample of solid gold is heated from 21oC to 32oC. 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 21oC to 36oC. 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, /\Hp = heat Problem 10.5, p. 302: The reaction that occurs in heat packs used for sports injuries is 4Fe(s) + 3O2(g) 2Fe2O3(s) /\H = -1652 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. • If a reaction is reversed, the sign of /\H is changed. • 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 10.9: The atmospheric CO2 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. (2nd Law of Thermodynamics) Example: (NH4)2CO3(s) 2NH3(g) + H2O(g) + CO2(g) H2O(s) H2O(l) H2O(g)
