calorimetry 2024

Calorimetry

Definition: Calorimetry is the measurement of the quantity of heat, which is the form of energy that flows from a hot body to a cold body.

Internal Energy: The sum of potential and kinetic energy of molecules is termed internal energy, leading to the concept of thermal energy—the total internal energy of all molecules in a substance. A hotter body contains more internal energy than a cooler one.

Units of Heat

• SI Unit: Joule (J).

• Calorie: The amount of heat required to raise the temperature of 1 gram of water by 1°C. 1 Calorie equals 4.2 Joules (1 Cal = 4.2 J).

Concept of Temperature

• Definition: Temperature is a measure of the degree of hotness or coldness of a body, indicating its thermal state and determining the direction of heat flow between two bodies in contact.

• Units: The SI Unit is Kelvin (K), while a common unit is degrees Celsius (°C): (T_k = t°C + 273).

Factors Affecting Heat Quantity

The quantity of heat energy absorbed to increase the temperature of a body depends on:

• Mass of the Body: Directly proportional to the mass (Q ∝ m).

• Increase in Temperature: Directly proportional to the temperature rise (Q ∝ Δt).

• Material of the Body: The specific heat capacity (c) influences the amount of heat absorbed (Q = cmΔt).

Heat Capacity and Specific Heat Capacity

• Heat Capacity (C'): Amount of heat required to raise the temperature of a body by 1°C. Given by (C' = [ \frac{Q}{Δt} ]), with units J/K.

• Specific Heat Capacity (C): Amount of heat required to raise the temperature of a unit mass of a body by 1°C, expressed as (C = [ \frac{Q}{m \times Δt} ]), with units J kg⁻¹ K⁻¹.

• Relationship: Heat Capacity = mass × specific heat capacity.

• Water's Specific Heat Capacity: 4200 J kg⁻¹ K⁻¹.

Calorimeter

• Definition: An instrument used to measure the heat gained or lost by a body.

Principle of Method of Mixtures

• Heat Exchange: The heat energy lost by a hot body is equal to the heat energy gained by a cold body, based on the law of conservation of energy.

• Mathematical Expression: (m₁c₁Δt = m₂c₂Δt).

Consequences of High Specific Heat Capacity of Water

• Moderate Climate: Coasts experience less extreme temperatures because of water's high specific heat capacity.

• Hot Water Bottles: Used for fomentation as water retains heat longer.

• Effective Coolant: Water removes heat from heated machine parts effectively due to its high specific heat capacity.

• Heat Reservoir: Useful in cold climates to prevent freezing of beverages.

• Frost Protection: Filling fields with water prevents freezing and protects crops during cold nights.

• Biological Importance: All plants and animals contain 80-90% water, helping to stabilize their body temperatures across seasons.

High and Low Heat Capacity Applications

• Thick Cooking Pan Base: Retains and evenly distributes heat.

• Electric Press: Thick base retains heat after switch-off.

• Calorimeter Construction: Made from thin copper sheet to minimize heat absorption and ensure accurate readings.

Change of Phase

• Definition: The transition between states of matter at constant temperatures due to heat exchange.

• Processes:

  • Melting: Solid to liquid (absorbs heat).

  • Freezing: Liquid to solid (rejects heat).

  • Vaporization: Liquid to gas (absorbs heat).

  • Condensation: Gas to liquid (rejects heat).

  • Sublimation: Solid to gas.

  • Solidification: Gas to solid.

Melting and Freezing Points

• Melting Point: Constant temperature where solids turn to liquids.

• Freezing Point: Constant temperature where liquids turn to solids.

• Expansion/Contraction: Most substances expand upon melting, except for ice, which contracts.

Heating Curve and Transition Points

• Heating Curve of Ice: Graph of temperature versus time shows different states and transitions—AB (liquid) and constant temperature during boiling at B.

• Volume Change: Most substances expand upon heating; water becomes significantly larger in vapor form compared to liquid.

Effects on Melting and Boiling Points

• Pressure Effects: Increasing pressure can lower melting points of certain substances and raise points for others.

• Impurity Effects: Adding impurities generally decreases melting points and increases boiling points.

Vaporization and Boiling

• Definition: Change from liquid to gas at a constant temperature; boiling point is the temperature at which this occurs.

• Heating Curve for Water: Similar to that of ice, reflecting heat absorption and state changes.

• Volume Change on Boiling: Expansion of liquids occurs, resulting in steam (1 cm³ water to 1760 cm³ steam).

Latent Heat and Specific Latent Heat

• Latent Heat: Heat absorbed or released during phase changes without temperature change.

• Specific Latent Heat (L): Given by (L = [ \frac{Q}{m} ]), measured in J/kg.

• Fusion of Ice: Heat required to melt ice at 0°C to water at the same temperature.

Natural Consequences of High Latent Heat of Fusion of Ice

• Slow Melting of Snow: Mountain snow melts gradually due to high latent heat.

• Water Bodies: Do not freeze immediately due to heat retention.

• Quick Cooling: Ice cools drinks faster than cold water.

• Temperature Drops: Surrounding air cools when ice melts due to heat absorption for phase change.

• Hail Storm Effects: Colder conditions after hail due to ice melting and absorbing heat.