Calorimetry measures heat transfer between systems, helping us understand how energy moves around. It's crucial for figuring out specific heat capacities and enthalpy changes during reactions or phase transitions. This knowledge is key in many real-world applications.

The first law of thermodynamics ties it all together, showing how heat transfer relates to changes in internal energy and work done. We use simple equations to calculate heat transfer during temperature changes and phase transitions, making complex concepts more manageable.

Calorimetry and Heat Transfer

Principles of calorimetry

• Measures heat transfer between systems based on conservation of energy principle
  • Heat lost by one system equals heat gained by another system in thermal equilibrium
• Enables determination of specific heat capacity of substances
  • Amount of heat required to raise temperature of 1 gram of substance by 1℃
• Investigates enthalpy changes during chemical reactions (combustion) or phase transitions (melting, boiling)
• Evaluates efficiency of heat engines (internal combustion engines) and thermal systems (heat exchangers)

First law in heat transfer

• Relates change in internal energy ($\Delta U$) to heat transferred ($Q$) and work done ($W$): $\Delta U = Q - W$
  • Internal energy depends on temperature, pressure, and volume of system
• Calculates heat transfer using $Q = mc\Delta T$
  • $m$: Mass of substance (grams or kilograms)
  • $c$: Specific heat capacity (J/g·℃ or J/kg·K)
  • $\Delta T$: Temperature change (℃ or K)
• Determines heat transfer during phase changes with $Q = mL$
  • $L$: Latent heat of fusion (melting/freezing) or vaporization (boiling/condensation) in J/g or J/kg

Phase Changes and Energy

Energy changes during phase transitions

• Phase transitions absorb or release latent heat at constant temperature
  • Latent heat of fusion: Energy to change substance from solid to liquid (or vice versa) at melting point
    • Example: Melting of ice at 0℃ absorbs 334 J/g
  • Latent heat of vaporization: Energy to change substance from liquid to gas (or vice versa) at boiling point
    • Example: Boiling of water at 100℃ absorbs 2260 J/g
• Calorimetry experiments measure temperature change of known mass of water during phase transition
  • Calculate latent heat using $Q = mL$
    • Example: Melting 10 g of ice in 100 g of water at 20℃ lowers temperature to 11.7℃

Interpretation of calorimetry data

• Specific heat capacity found by measuring temperature change for known heat added/removed
  • Calculate using $c = \frac{Q}{m\Delta T}$
    • Example: Heating 50 g of aluminum from 20℃ to 70℃ requires 1130 J, so $c = \frac{1130 J}{50 g \times 50℃} = 0.452 J/g·℃$
• Latent heat determined by measuring heat transfer during constant-temperature phase change
  • Calculate using $L = \frac{Q}{m}$
    • Example: Condensing 5 g of steam at 100℃ releases 11300 J, so $L = \frac{11300 J}{5 g} = 2260 J/g$
• Interpret data by identifying initial/final temperatures, mass, and heat transferred
  • Use equations to calculate specific heat capacity or latent heat
  • Compare results to literature values to validate experiment