• Heat capacity (C): heat absorbed per degree (J/C or J/K)

○ Extensive property: depend on amount of substance

• Specific heat capacity (cp): heat capacity per gram (J/C·g or J/K)

○ Amount of heat required to change one gram of a substance temperature by one degree C or K

• Every substance has its own specific heat capacity

○ Cp of water is 4.18 J/C·g → requires 4.184 J (1 cal) of energy to heat a gram by one degree

• Molar heat capacity: heat capacity per mol (K/C mol or K/K mol)
• Specific and Molar heat capacity are intensive properties: independent of the amount (of substance)

Heat Transfer Equations

• qA = -qB → heat lost = – heat gained

○ qsystem = -qsurroundings; qsolution = -qreaction

• q = the amount of heat absorbed or released

○ Note: “molar heat of solution” = q

• Signage of Heat Transfer Equations:

○ Do q = mcpΔT and keep q always positive initially

○ Add a positive or negarive sign to the q value on the knowledge that…

■ If the temp of the water went down, then the reaction was endothermic and qsol = –

■ If the temp of the water went up, then the reaction was exothermic and qsol = +

•  ΔHrxn =

○ Important: ΔH will be per 1 mole of substance → divide moles in sample by moles (coefficient) in the balanced equation

• Questions involving specific heat → the amount of heat (J) gained/lost by a sample (q) can be determined by the formula: q = mcpΔT or ncpΔT

○ m = mass of sample

○ C = specific heat

○ Questions involving two substances: Do two mcats → mcΔT = – (mcΔT)

■ Ex:

○ Questions involving ΔT

■ If moles increases → more moles reacting so final temp will be higher → q increases b/c ΔT is greater

■ If heat is lost to the surroundings (ex: air) → q decreases b/c ΔT is smaller → (if exo) ΔH will be less negative

• Example Question Proccess
1. Water is heated by an external source (ex: combustion)
• Since water is only thing undergoing temp change, only use the mass of water
1. Chemicals are mixed in a solution and a temp change occurs in a solution (calorimetry)
• Use temp change and cp of the solution, and the mass of the solution (mass of solute + solvent)