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THERMOCHEMISTRY

THERMOCHEMISTRY. Chapter 11. The amount of energy needed to to increase the temperature of an object exactly 1 0 C is the heat capacity of that object. ( J/ 0 C ).

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THERMOCHEMISTRY

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  1. THERMOCHEMISTRY Chapter 11

  2. The amount of energy needed to to increase the temperature of an object exactly 10C is the heat capacity of that object. (J/0C) The specific heat capacity or simply specific heat of a substance is the amount of heat/ energy needed to raise the temperature of 1g of the substance 10C. (J/g0C) HEAT CAPACITY AND SPECIFIC HEAT

  3. Calculating Heat Capacity • The heat capacity of an object is equal to its specific heat times its mass. • EX. The heat capacity of a 5 gram piece of pure aluminum is equal to: 5g X 0.90J/g0C = 4.50 J/0C

  4. Calculating Specific Heat • C = __q___ = m X ΔT = heat(joules or calories) mass(g) X change in temperature (0C)

  5. Sample Problem • How much heat is required to raise the temperature of 250 g of mercury 52 0C? The specific heat for mercury is: 0.14 J/g0C

  6. SOLVE for q(heat) • C = __q___ m X ΔT • Rearrange the specific heat formula to solve for q. • q = C x m x ΔT NOW PLUG AND CHUG…

  7. ANSWER • q = C x m x ΔT • q = 0.14 J x 250g x 520C = g 0C = 1,800 J or 1.8kJ

  8. CALORIMETRY • Calorimetry is the accurate and precise measurement of heat change for chemical and physical processes. • In calorimetry, the heat released by the system is equal to to the heat absorbed by its surroundings. • What law describes this relationship?

  9. Calorimeter • To measure heat changes accurately and precisely, the process must be carried out in an insulated container. • The insulated device used to measure the absorption or release of heat in chemical or physical processes is called a calorimeter.

  10. Heat of Reaction • A heat of reaction is the heat change for the equation exactly as it is written. • For systems at constant pressure, the heat content is the same as a property called the Enthalpy (H) of the system. (q = ΔH)

  11. Thermochemical Equations • You can treat heat change in a chemical reaction like any other reactant product in a chemical equation. • A chemical equation that includes the heat change is referred to as a thermochemical equation.

  12. ΔH is Positive

  13. ΔH is Negative

  14. Types of Thermochemical Equations Endothermic (ΔH is positive): Na2CO2 + H2O + CO2 + 129kJ NaHCO3 Exothermic (ΔH is negative): CaO + H2O Ca(OH)2 + 65.2KJ

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