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Entropy Change During Phase Transitions in General Chemistry

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  • What is entropy (S)?

    Entropy is a measure of disorder or randomness in a system.

  • What is enthalpy of vaporization (ΔHvap)?

    Enthalpy of vaporization is the energy required to convert 1 mole of a liquid to a gas at constant temperature and pressure.

  • What is the boiling point in the context of phase changes?

    The boiling point is the temperature at which a liquid turns into a gas.

  • How do you convert Celsius to Kelvin?

    Add 273.15 to the Celsius temperature to convert it to Kelvin.

  • What is the formula for entropy change (ΔS) during a phase transition?

    ΔS = \(\frac{q_{rev}}{T}\), where qrev is the heat absorbed reversibly and T is the absolute temperature in Kelvin.

  • How do you calculate entropy change when 1 mole of methanol vaporizes at its boiling point?

    ΔS = ΔHvap / T, where ΔHvap is enthalpy of vaporization in joules and T is temperature in Kelvin.

  • What is the boiling point of methanol in Kelvin if it is 64.6°C?

    T = 64.6 + 273.15 = 337.75 K

  • Convert 35.2 kJ/mol enthalpy of vaporization to joules.

    35.2 kJ/mol × 1000 J/kJ = 35,200 J/mol

  • Calculate the entropy change for methanol vaporization using ΔH = 35,200 J/mol and T = 337.75 K.

    ΔS = 35,200 J/mol ÷ 337.75 K = 104.2 J/mol·K

  • Is the entropy change positive or negative when methanol vaporizes?

    The entropy change is positive, indicating increased disorder as methanol vaporizes.