Chapter Menu Energy and Chemical Change Section 15.1Section 15.1Energy Section 15.2Section 15.2 Heat Section 15.3Section 15.3 Thermochemical Equations Section 15.4Section 15.4 Calculating Enthalpy Change Section 15.5Section 15.5Reaction Spontaneity Exit Click a hyperlink or folder tab to view the corresponding slides.

Section 15-1 Section 15.1 Energy Define energy. temperature: a measure of the average kinetic energy of the particles in a sample of matter Distinguish between potential and kinetic energy. Relate chemical potential energy to the heat lost or gained in chemical reactions. Calculate the amount of heat absorbed or released by a substance as its temperature changes.

Section 15-1 Section 15.1 Energy (cont.) energy law of conservation of energy chemical potential energy heat calorie joule specific heat Energy can change form and flow, but it is always conserved.

Section 15-1 The Nature of Energy Energy is the ability to do work or produce heat.Energy Two forms of energy exist, potential and kinetic. Potential energy is due to composition or position. Kinetic energy is energy of motion.

Section 15-1 The Nature of Energy (cont.) The law of conservation of energy states that in any chemical reaction or physical process, energy can be converted from one form to another, but it is neither created nor destroyed—also known as the first law of thermodynamics.law of conservation of energy

Section 15-1 The Nature of Energy (cont.) Chemical potential energy is energy stored in a substance because of its composition, arrangement, and bonds.Chemical potential energy Chemical potential energy is important in chemical reactions. Heat is energy that is in the process of flowing from a warmer object to a cooler object.Heat q is used to symbolize heat.

Section 15-1 Measuring Heat A calorie is defined as the amount of energy required to raise the temperature of one gram of water one degree Celsius.calorie FoodCalories kilocalories(1000 calories).Food is labeled in Calories, which are really kilocalories(1000 calories). A joule is the SI unit of heat and energy, equivalent to calories.joule 1 cal = J

Section 15-1 Measuring Heat (cont.)

1) A candy bar contains 320 Calories. How many joules of energy is this? 320 nutritional Cal = 320,000 calories 320,000 cal x J/cal = 1.34x10 6 J

Section 15-1 Specific Heat The specific heat of any substance is the amount of heat required to raise one gram of that substance one degree Celsius.specific heat Some objects require more heat than others to raise their temperature. A higher specific heat means it takes more energy to change the temperature.

Section 15-1 Specific Heat If you have 10.0 g blocks of Al, Ca, and Fe all at the same temperature, and you add 25 J of energy to each, which will have the highest final temperature? The Fe, since it has the lowest specific heat of the three.

Section 15-1 Specific Heat (cont.) Calculating heat absorbed and released q = c × m × ΔT q = heat absorbed or released c = specific heat of substance m = mass of substance in grams ΔT = change in temperature in Celsius

Section 15-1 Specific Heat How much energy is needed to heat a 2500 g ingot of magnesium from 20.0 to 50.0 o C? q = (1.023 J/g o C)(2500g)(30.0 o C) q = 77,000 J

Section 15-1 Specific Heat If you transfer 1750 J of heat to 150. g of water at 20.0 o C, what will the final temperature be? 1750 J = (4.184 J/g o C)(150. g)(∆T) ∆T = 2.79 o C T final = 20.0 o o = 22.8 o C

A.A B.B C.C D.D Section 15-1 Section 15.1 Assessment The heat required to raise one gram of a substance by one degree Celsius is called ____. A.joule B.calorie C.specific heat D.energy

A.A B.B C.C D.D Section 15-1 Section 15.1 Assessment Which of the following is an example of chemical potential energy? A.the moon orbiting Earth B.a car battery C.a compressed spring D.a roller coaster at the top of a hill

End of Section 15-1

Section 15-2 Section 15.2 Heat Describe how a calorimeter is used to measure energy that is absorbed or released. pressure: force applied per unit area Explain the meaning of enthalpy and enthalpy change in chemical reactions and processes.

Section 15-2 Section 15.2 Heat (cont.) calorimeter thermochemistry system surroundings The enthalpy change for a reaction is the enthalpy of the products minus the enthalpy of the reactants. universe enthalpy enthalpy (heat) of reaction

Section 15-2 Calorimetry A calorimeter is an insulated device used for measuring the amount of heat absorbed or released in a chemical reaction or physical process.calorimeter

Section 15-2 Chemical Energy and the Universe The system is a specific part of the universe that contains the reaction or process you wish to study.system The surroundings are everything else in the universe other than the system.surroundings

Section 15-2 Chemical Energy and the Universe (cont.) Enthalpy (H) can be thought of as the heat content of a system at constant pressure.Enthalpy Enthalpy (heat) of reaction is the change in enthalpy during a reaction symbolized as ΔH rxn.Enthalpy (heat) of reaction ΔH rxn = H products – H reactants

Section 15-2 Chemical Energy and the Universe (cont.) Enthalpy changes for exothermic reactions are always negative. (- ΔH rxn ) think: the system loses energy the surroundings gain energy (warmer) Enthalpy changes for endothermic reactions are always positive. (+ΔH rxn ) think: the system gains energy the surroundings lose energy (cooler)

Section 15-2 Chemical Energy and the Universe (cont.)

Section 15-2 Chemical Energy and the Universe (cont.)

A.A B.B C.C D.D Section 15-2 Section 15.2 Assessment In thermochemistry, the specific part of the universe you are studying is called ____. A.system B.area C.enthalpy D.surroundings

A.A B.B C.C D.D Section 15-2 Section 15.2 Assessment What is the heat content of a system at constant pressure called? A.heat of reaction B.heat of the system C.enthalpy D.entropy