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Energetics

Standard conditions and the standard enthalpy change

  • 3 things to know
  • Unit AS 2

Overview

Standard conditions of pressure and temperature used in thermochemistry, term standard enthalpy change and units in which a standard enthalpy change is quoted.

What you need to know

Answer each one before you reveal it.

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Key term

State the standard conditions of pressure and temperature used in thermochemistry.

Key term

What temperature in degrees Celsius corresponds to 298 K?

Key term

State the units in which a standard enthalpy change is quoted.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the standard conditions of pressure and temperature used in thermochemistry.

    Model answer

    The standard conditions are a pressure of 100 kPa and a temperature of 298 K.

  2. 2

    What temperature in degrees Celsius corresponds to 298 K?

    Model answer

    298 K corresponds to 25 °C.

  3. 3

    Define the term standard enthalpy change.

    Model answer

    The standard enthalpy change is the enthalpy change for a reaction measured at 100 kPa and 298 K with every substance in its standard state.

  4. 4

    State the units in which a standard enthalpy change is quoted.

    Model answer

    A standard enthalpy change is quoted in kJ mol⁻¹.

  5. 5

    What does the superscript symbol in ΔHӨ tell you?

    Model answer

    It shows that the value refers to standard conditions with all substances in their standard states.

  6. 6

    What is meant by the standard state of a substance?

    Model answer

    The standard state is the physical form in which the substance is most stable at 100 kPa and the stated temperature.

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