SCH4U - Chemistry 12 (2024-25) - A

• Specific heat capacity (c) is the amount of energy (Q) it takes to raise 1 gram of a substance by 1 ˚C
• c = Q /(m*ΔT)
• The transfer of heat (Q) can be calculated if the mass of the substance (m), specific heat capacity (c), and change in temperature (ΔT) are known.  The formula is: Q = m x c x ΔT
• When a system gains heat, Q will be positive, and when it loses heat, Q is negative.
• A system with a negative Q is exothermic (Lost heat). A system with a positive Q is endothermic (added heat)
• Q represents the change in heat, which is also the change in enthalpy (ΔH), therefore Q = ΔH.
• Calorimetry can be used to determine the amount of heat lost and gained in a system, by measuring the change in temperature using a calorimeter.
• We can assume that all the heat released by a system is gained by the surroundings.

Q_system = - Q_surroundings

ΔH_system = - ΔH_surroundings

• Molar enthalpy is the change in enthalpy that occurs when 1 mole of a substance reacts
• To calculate molar enthalpy, ΔH_{molar ,} the enthalpy (ΔH) of the reaction is divided by the number of moles ΔH_molar = ΔH / n
• Reminder: n = m_s / M_m