heat and temperature

Heat and Temperature

  • Heat Energy

    • Heat energy is required to change the states of substances, such as melting and boiling.

    • Process can disrupt forces of attraction at a molecular level.

  • Endothermic Process

    • An endothermic process absorbs heat from its surroundings.

    • Example:

      • When you hold a piece of ice in your hand, the ice absorbs heat from your hand to melt, causing the temperature of your hand to decrease.

      • This results in a feeling of coldness in the hand.

Heating Curve of Water

  • Temperature vs. Time Graph

    • A heating curve for water shows how temperature changes with time as it undergoes different phases.

    • Key Points in the Heating Curve:

      1. Solid Warming (a-b): The temperature of solid ice increases.

      2. Melting/Freezing (b+c): Ice melts into water at 0°C.

      3. Liquid Warming (c-d): The temperature of liquid water increases until it reaches 100°C.

      4. Boiling/Condensing (d-e): Water boils into steam at 100°C.

      5. Gas Warming (e-f): The temperature of steam continues to increase beyond 100°C.

  • Graph Representation

    • The graph typically has temperature (°C) on the vertical axis and time on the horizontal axis.

Comparison of Butanol and Ethanol

  • At 60°C:

    • Butanol Vapor Pressure (Pₐᵣₐₚ) = 103 torr

    • Ethanol Vapor Pressure (Pₐᵣₐₚ) = 353 torr

  • Intermolecular Forces:

    • Strongest Forces: Butanol

      • Butanol has stronger intermolecular forces compared to Ethanol.

  • Heat of Vaporization (ΔHᵥₐₚ):

    • Highest ΔHᵥₐₚ: Butanol

      • Butanol requires more energy to vaporize due to stronger intermolecular forces.

  • Rate of Evaporation:

    • Fastest Rate of Evaporation: Ethanol

      • Ethanol has a higher vapor pressure, indicating it evaporates more quickly.

  • Boiling Under Reduced Pressure:

    • If both Butanol and Ethanol are placed in a flask attached to a vacuum pump and the pressure is reduced to 200 torr:

      • Ethanol will boil because its vapor pressure (353 torr) is greater than the surrounding pressure (200 torr).

      • Butanol will not boil since its vapor pressure (103 torr) is lower than the surrounding pressure (200 torr).

    • Boiling Condition:

      • A substance will boil when its vapor pressure (Pₐᵣₐₚ) exceeds the surrounding pressure (Pₛᵘᵗₕ) - hence the requirement for boiling is: P{a, rap} > P{sur}

    • For Ethanol:

      • P_{sur} = 200 ext{ torr}

      • P_{a, rap} = 353 ext{ torr}