Calorimetry Part 1

Calorimetry Overview

  • Definition: Calorimetry is the measurement of heat changes (q). In constant pressure situations, it is represented as ΔH (enthalpy change).

Key Concepts

Specific Heat

  • Definition: Amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

  • Symbol: Lowercase s.

  • Units: Energy units per gram °C (calories and joules).

    • Specific heat of water is 1.000 cal/g°C or 4.184 J/g°C.

  • Dietary Calories: Capital C calorie (kcal) is equivalent to 1000 scientific calories (cal).

Heat Capacity

  • Definition: Heat capacity (C) is the product of mass (m) and specific heat (s). An extensive property.

    • Equation: C = m × s (for pure substances).

    • Units: Joules/°C.

  • Usage: Can apply to any material, including mixtures.

Heat Transfer

  • Heat Transfer Equation: Q = m × s × ΔT

    • ΔT: Change in temperature (T_{final} - T_{initial}).

  • Heat flows from hot to cold, reaching thermal equilibrium when temperatures equalize.

Conducting Calorimetry Experiments

  • Isolated System: Should remain isolated for accurate results (e.g. using Styrofoam cups).

  • Master Equation: Q_system = Q_1 + Q_2 + ... + Q_n = 0

    • Components must be identified and recorded in the equation.

Example Problems

Heat Capacity Calculation

  • Example: Determine heat capacity of 53 grams of water using C = m × s.

Temperature Change Calculation

  • Example: Calculate heat absorbed by 20g water from 25°C to 90°C using Q = m × s × ΔT.

Important Notes on Temperature Scales

  • The change in temperature (ΔT) can be calculated in either Celsius or Kelvin, as the magnitude remains the same.

Experimental Setup for Calorimetry

  • Components: Identify what materials are included in the system (water, metal, calorimeter, air, etc.)

  • Setting Up the Equation: Establish equations for heat lost/gained by each component, noting that the total must equal zero for isolated systems.

  • Example Sketch: Sketching scenarios with the materials in the calorimeter helps identify heat transfers and components.

  • Initial temperature values for materials must be established for calculations.

Common Mistakes

  • Be cautious of significant figures and signs in calculations.

  • Ensure units cancel correctly when performing dimensional analysis.

Bomb Calorimetry

  • Definition: A type of calorimetry used for measuring heat changes in reactions at high pressures, typically combustion reactions.

  • Components include the calorimeter itself, the reaction, heat capacity, and sometimes water.

  • Key Equation: Q_system = Q_reaction + Q_calorimeter = 0.

General Notes on Bomb Calorimetry

  • Use heat capacity of the calorimeter (C) for calculations.

  • Understand that calorimetry results can yield values normalised to energy per gram or per mole for standardization.

  • Experimental temperature changes are critical for calculations of energy changes.

Tips for Proficiency in Calorimetry Problems

  • Develop mastery of defining systems and identifying components to craft master equations accurately.

  • Practice different formats of calorimetry problems and common mathematical manipulations.