SCH4U - Thermochemistry

Enthalpy (H) 

heat energy ΔH (delta H) ← change in heat energy during a reaction

If ΔH is negative (−) → the reaction releases heat

exothermic

If ΔH is positive (+) → the reaction absorbs heat

endothermic

Molar enthalpy 

how much heat is released or absorbed per mole of a substance 

What does this formula mean: ΔH = q/n

• ΔH\Delta HΔH = molar enthalpy (kJ/mol)

• q = total heat energy absorbed or released (kJ)

• n = moles of substance reacted or produced (mol)

What does this formula mean: q=mcΔT

• m = mass of the water or solution (g)

• c = specific heat capacity (usually 4.18 J/g°C for water)

• ΔT\Delta TΔT = temperature change (°C)

Then convert q into kJ (divide by 1000).

What are the two formulas to find moles? 

n = mass/molar mass & n = c x V (for solutions, where c is concentration in mol/L and V is volume in L)