Energy and Physical Changes – Part II Heating Curves, Specific Heat Capacity, Molar Heat, Calculations of Physical Energy Changes

Heating Curves a graph that shows the temperature vs. either time or energy B. ENDOthermic heating curves positive slope because heat is absorbed shows the transformation: solid → liquid → gas

Heating Curves – Endothermic   A: ↑ KE; PE constant C: ↑ KE; PE constant B: ↑ PE; KE constant D: ↑ PE; KE constant E: ↑ KE; PE constant

Heating Curves C. EXOthermic heating curves negative slope because heat is released shows the transformation: gas → liquid → solid

Heating Curves – Exothermic A: ↓ KE; PE constant C: ↓ KE; PE constant B: ↓ PE; KE constant D: ↓ PE; KE constant E: ↓ KE; PE constant

Specific Heat Capacity the amount of heat necessary to convert 1 gram of a substance 1 °C unit = cal/g x °C or J/g x °C unique to each substance (and phase of substance) ex: specific heat capacity for liquid water = 4.18 J/g x °C; specific heat capacity for ice = 2.09 J/g x °C symbol = c H2O has the highest specific heat capacity among any common substance

Molar Heat Molar Heat of Fusion the amount of heat necessary to melt (or freeze) 1 mole of a substance at its melting point unique to each substance symbol = ΔHfus only applies when there is no temperature change…describes potential energy and NOT kinetic energy

Molar Heat Molar Heat of Vaporization the amount of heat necessary to evaporate (or condense) 1 mole of a substance at its boiling point unique to each substance symbol = ΔHvap only applies when there is no temperature change…describes potential energy and NOT kinetic energy

Calculations of Energy Changes q = mcΔT used only for temperature changes! q = the amount of heat absorbed or released (in cal or J) a gain or loss of heat + q = heat absorbed = endothermic; - q = heat released = exothermic m = the mass of substance (in grams) ΔT = the change in temperature Tfinal - Tinitial

Calculations of Energy Changes B. q = molΔHfus used only when the temperature is constant q = the amount of heat absorbed or released (in cal or J) for the substance to convert between the solid and liquid phases a gain or loss of heat mol = the moles of substance (divide given mass by molar mass) ΔHfus = the molar heat of fusion (a constant for each substance)!

Calculations of Energy Changes C. q = molΔHvap used only when the temperature is constant q = the amount of heat absorbed or released (in cal or J) for the substance to convert between the liquid and gas phases a gain or loss of heat mol = the moles of substance (divide given mass by molar mass) ΔHvap = the molar heat of vaporization (a constant for each substance)!

q = mc∆T q = molΔHfus 4 q = molΔHvap 5 q = mc∆T