Chemistry Chapter: Heat and Phase Changes

Exothermic and Endothermic Processes

• Condensation is an exothermic process, releasing heat.
• Fusion (melting), vaporization (boiling), and sublimation absorb heat, classifying them as endothermic.
• Crystallization (freezing), condensation, and deposition release heat, thus they are exothermic.

Specific Heat Calculation

• To calculate the specific heat of an unknown metal:
  • A 50g piece of metal at 50°C is placed in 50g of water at 0°C, reaching thermal equilibrium at 10°C.
  • Using the formula for heat transfer, where heat lost by metal equals heat gained by water, the specific heat of the metal is determined to be 0.25 cal/g°C.

Heat Requirement for Water Temperature Change

• To find the heat needed to raise the temperature of 50g of H₂O from 10°C to 79.4°C:
  • Apply the formula q = mcΔT, where m is mass, c is specific heat, and ΔT is the temperature change.
  • The required heat calculated is 3470 cal.

Phase Changes and Thermodynamic Variables

• The variables ΔH (change in enthalpy) and ΔS (change in entropy) are critical in determining phase changes in thermodynamics.
• ΔH > 0 signifies endothermic processes, where heat is absorbed.
• Important to remember the relationship between phase changes and changes in energy and disorder.

This quiz explores the concepts of exothermic and endothermic processes, specific heat calculations, and the heat required for temperature changes in water. Test your understanding of how heat transfer and phase changes operate in various chemical processes.