Topic 8 - ENERGETICS
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What is the definition of standard enthalpy of formation?
The enthalpy change when: - One mole of a substance - is formed from its elements - in their standard states (at 298K and 100kPa)
What is the definition of standard enthalpy of combustion?
The enthalpy change when: - One mole of a substance - is completely oxidised in excess oxygen - at standard conditions (298K and 100kPa)
What is the definition of standard enthalpy of neutralisation?
The enthalpy change when: - One mole of water forms - By the neutralisation of an acid and alkali - At standard conditions (298K and 100kPa)
What is the formula for heat energy produced (Q)?
Q=mc∆T where: m = mass c = specific heat capacity ∆T = change in temperature
What is the formula for enthalpy of a reaction?
∆H=-Q/moles
What are the two main errors that occur during calorimetry?
• Heat energy is lost to surroundings • Less energy is released
What is the effect if heat energy is lost during calorimetry?
• ∆T would be less positive • Q would be less positive • ∆H would be less negative
What is the effect if less energy is released during calorimetry?
∆T would be less positive - Q would be less positive - ∆H would be less negative
What is Hess’ Law?
∆H for a reaction is independent of the route taken
What are the 4 possible reactions when calculating Hess’ Law?
• Enthalpy of formation • Enthalpy of combustion • Enthalpy of neutralisation • Dissolving