measuring heat changes
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Measuring heat changes. Section 11.2. After reading Section 11.2, you should know:. How to write or interpret a thermochemical equation How to calculate heat changes in a chemical or physical process. Calorimetry.

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after reading section 11 2 you should know
After reading Section 11.2, you should know:
  • How to write or interpret a thermochemical equation
  • How to calculate heat changes in a chemical or physical process
calorimetry
Calorimetry
  • Calorimetry – the accurate and precise measurement of heat changes which occur during chemical and physical processes.
enthalpy
Enthalpy
  • Enthalpy (H) – measure of the heat content of a system.
  • ∆H – change in enthalpy at constant pressure
    • For reactions which take place at constant pressure, the terms heat and enthalpy are used interchangeably, that is, q = ∆H.
  • q = ∆H = (m)(Cp)(∆T)
calorimeters
Calorimeters
  • Coffee cup calorimeter – an insulated device used to measure the absorption or release of heat of a reaction at constant pressure.
  • Bomb calorimeter – used for measuring heat released when a compound is burned at constant volume.
thermochemical equations
Thermochemical Equations
  • Thermochemical equation – an equation which includes the heat of the reaction
    • The physical state of all reactants and products must also be stated
    • The energy absorbed or released in a chemical equation can be expressed in two different ways:
      • As a reactant or product or
      • Using the symbol ΔH
thermochemical equations7
Thermochemical Equations

Endothermic reaction

(heat is a absorbed, so it is a reactant):

2 NaHCO3(s) + 129 kJ → Na2CO3(s) + CO2(g) + H2O(g)

OR

2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) ∆H = +129 kJ

thermochemical equations8
Thermochemical Equations

Exothermic reaction

(heat is given off, so it is a product):

CaO(s) + H2O(l) → Ca(OH)2(s) + 65.2 kJ

OR

CaO(s) + H2O(l) → Ca(OH)2(s) ∆H = − 65.2 kJ

after reading section 11 2 you should know9
After reading Section 11.2, you should know:
  • How to write or interpret a thermochemical equation
  • How to calculate heat changes in a chemical or physical process
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