11.3 – NOTES Combustion

Exothermic reaction, therefore heat is released B.6 Combustion Burning is combustion CxHy + O2  CO2 + H2O + energy   Exothermic reaction, therefore heat is released

Specific heat capacity Shortened to specific heat The amount of energy needed to raise 1 gram of something by 1°C Water’s is 4.18 J/(gC)

Calculating energy using specific heat The equation for these problems is Q = m * C * T Q = thermal energy/heat Joules (J), kilojoules (kJ) or calories (cal)   m = mass of the object in grams (g) C = specific heat (J/g°C or cal/g°C) ΔT = change in temperature = Tfinal - Tinitial (°C) Δ = delta = change in _____________

Examples How many joules of energy are given off when heating 12.5 g of water from 10 °C to 25 °C?   ~ 783.75 J

What is the specific heat of a substance that releases 250 J of energy when 10 g are heated 35°C?   ~c = .714 J/g°C

Heat of combustion Amount of energy given off when something burns kJ/gram or J/gram   Molar heat of combustion Amount of heat involved when burning 1 mole of something Remember, 1 mole = 6.02 x 1023 kJ/mol or J/mol