Chem 105 middterm 3 (lecture 2) caloriemetry

Specific Heat of Water (l)

4.18 J/(g·°C) or 4.18 kJ/(kg·°C). Water has an unusually high specific heat capacity.

Specific Heat vs. Slope on Heating Curve

A higher specific heat capacity means a smaller/flatter slope on a temperature vs. heat graph (requires more energy to raise temp).

Density of Liquid Water

1.00 g/mL (or 1.00 kg/L). Allows converting volume in mL directly to mass in grams.

Calorie to Joule Conversion

1 calorie = 4.18 Joules.

Nutritional Calorie (Calorie)

1 Calorie (capital C) = 1 kilocalorie (kcal) = 1000 small calories.

Five Stages of Water Heating Curve

1. Heating ice, 2. Melting ice (fusion), 3. Heating liquid water, 4. Boiling water (vaporization), 5. Heating steam.

Choosing Heat Equations: Temp Change vs. Phase Change

Use q = m·c·ΔT when temperature changes within a phase; use q = n·ΔH (or m·ΔH) during a phase change at constant temp.

Heat Capacity Equation (Mass-based)

q = m c_p ΔT (where m is mass in grams, c_p is specific heat capacity in J/g°C).

Heat Capacity Equation (Molar)

q = n c_p,n ΔT (where n is moles, c_p,n is molar heat capacity in J/mol°C).

Total Heat Capacity Equation

q = C_p ΔT (where C_p is the total heat capacity of an object/calorimeter in J/°C or kJ/°C).

Temperature Change in ΔT

ΔT = T_final - T_initial. Can be in Celsius or Kelvin since 1°C degree size equals 1 K degree size.

Principle of Calorimetry

Energy conservation: -q_lost = q_gained (e.g., -q_metal = q_water).

Calorimetry Formula for Unknown Metal

• (m_m * c_m * ΔT_m) = m_w * c_w * ΔT_w

Bomb Calorimeter Heat Equation

q = C_calorimeter * ΔT (uses the total combined heat capacity of the entire calorimeter system).

Sign of Reaction Enthalpy (ΔH)

Negative (-ΔH) for exothermic reactions (releases heat); Positive (+ΔH) for endothermic reactions (absorbs heat).

Stoichiometric Reaction Enthalpy

The given ΔH_rxn corresponds directly to the exact molar coefficients written in the balanced chemical equation.

Vaporization vs. Fusion Energy Comparison

Heat of vaporization (boiling) requires much more energy than heat of fusion (melting)—for water, about 8x as much energy.

Specific Heat of Ice

2.11 J/(g·°C)

Specific Heat of Steam

2.09 J/(g·°C)