Chapter 11

1. Chapter 11 Thermochemistry

2. 11.1 – The Flow of Heat Chemistry • Thermochemistry: • The study of heat changes that occur through chemical reactions. • Energy: • The capacity for doing work or supplying heat. • Chemical Potential Energy: • Energy stored within the structural units of chemical substances. • Example: Gasoline • Heat: • (q): energy that transfers from one object to another because of temperature differences between them. • Only changes in heat can be detected – not heat itself • Heat always flows from hot to cold until equilibrium is reached.

3. Universe: • System and surroundings • System: • Part of the universe where you are focusing your attention. • Surroundings: • Everything else in the universe. • Why do we need to know these three? • Thermochemistry is the study of the flow of heat from the system to the surroundings, or vice versa.

4. Law of Conservation of Energy: • Energy is neither created or destroyed. • All energy is either work, stored energy or heat. • Endothermic process: • Absorbs heat from surroundings • Heat flows into system from surroundings • +q • Exothermic process: • Releases heat from surroundings • Heat flows into surroundings from system • -q

5. Calories • Heat is measured in calories. • calorie: • Quantity of heat needed to raise the temperature of 1 g of pure water 1°C. • Calorie ≠ calorie • 1 Calorie = 1 kilocalorie = 1000 calories • Joule: • SI unit of heat and energy • 1 cal = 4.18 J *Memorize this!!

6. Heat Capacity: • The amount of heat needed to increase the temperature of an object exactly 1°C. • Specific Heat Capacity: • a.k.a. specific heat: the amount of heat it takes to raise the temperature of 1 g of the substance 1°C. • Explain this: • Mark Twain wrote: “the coldest winter I ever spent was the summer in San Fransico.”

7. .. • Q=mc∆T • (In your book it is c = q / m∆T) • Sample: • The temperature of a piece of copper with a mass of 95.4 g increases from 25°C to 48°C when the metal absorbs 849J. What is the specific heat? • C = 0.39 J/g°C

8. 11.2 • Calorimetry: • The accurate and precise measurement of heat change for chemical and physical processes. • Calorimeter: • The insulated device used to measure the absorption or release of heat in chemical or physical processes. • Enthalpy: (H) • For systems at constant pressure, this is the heat content • ∆H is negative for exothermic reaction and ∆ H is positive for endothermic reaction.

9. Thermochemical equations: • An equation that includes the heat change • CaO(s) + H2O(l) → Ca(OH)2(s) + 65.2kJ • Heat of Reaction: • The heat of change for the equation exactly as it is written. • Heat of Combustion: • The heat of reaction for the complete burning of one mol of a substance. • Brown fat vs. normal fat

10. 11.3 • When you put ice in a drink, what happens? • Molar heat of fusion: • ∆Hfus: the heat absorbed by one mol of a substance in melting from a solid to a liquid. • Molar heat of solidification: • ∆Hsolid: the heat lost when one mole of a liquid solidifies at a constant temperature. • ∆Hfus = ∆Hsolid for the same substance

11. Molar heat of vaporization: • ∆Hvap: amount of heat necessary to vaporize one mole of a given liquid. • Molar heat of condensation: • ∆Hcond: amount of heat released when 1 mol of vapor condenses

12. Heat Curve 5. T e m p e r a t u r e gas 4. l – g 3. • Q = mc∆T • Q = mHf • Q = mc∆T • Q = mHv • Q = mc∆T liquid 2. s – l 1. solid Water ∆Hvap = 40.7 kJ/mol ∆Hfus = 6.01 kJ/mol Found on Table 11.5 Heat supplied