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Energetics and Thermodynamics

Enthalpy Change and Standard Conditions

  • 3 things to know
  • Papers 1 and 3

Overview

Exothermic and endothermic changes, standard conditions, and the standard enthalpy definitions.

What you need to know

Answer each one before you reveal it.

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Key term

What is enthalpy change (ΔH)?

Key term

Besides pressure, what else must be stated for standard conditions?

Key term

How is a standard enthalpy change at 298 K symbolised?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is enthalpy change (ΔH)?

    Model answer

    The heat taken in or given out when pressure is held constant

  2. 2

    Under what conditions is enthalpy change measured?

    Model answer

    Constant pressure

  3. 3

    What pressure is specified for standard conditions?

    Model answer

    100 kPa

  4. 4

    Besides pressure, what else must be stated for standard conditions?

    Model answer

    A temperature (e.g. 298 K)

  5. 5

    How is a standard enthalpy change at 298 K symbolised?

    Model answer

    ΔH°₂₉₈ (with the theta symbol and temperature subscript)

  6. 6

    What does the term exothermic mean in relation to a reaction?

    Model answer

    A reaction that releases heat energy to the surroundings (negative ΔH)

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