*
*
*Calorimetry is a laboratory technique
used to measure heat flow
*Based on the law of conservation of
energy
*Idea that the heat released by the
system equals heat absorbed by the
surroundigs or vise versa; q = -q
*
*An ice cube is added to a warm cup of
water.
*The amount of heat used to melt the ice
cube is the same amount of heat lost by
the warm water.
*
*insulated device used
to measure heat flow
*Either measure the
heat absorbed or
released during
chemical/physical
change
*
*Enthalpy (H) is the heat content of a system at
constant pressure
*Thermochemistry uses the change in
enthalpy(H) to study heat changes
*At constant pressure, q = H
*Heat of reaction (∆Hrxn) is the change of
enthalpy in a chemical reaction
*
*All chemical and physical changes release or
absorb heat
*Exothermic: releases heat; q is neg; H is neg
*Endothermic; absorbs heat; q is pos; H is pos
*
*Equation that includes the physical states of all reactants
and products (1 atm, 25oC) and the energy change, H
*Endo
*NH4NO3(s)  NH4+(aq) +
*Exo
*CaO(s) +
NO3-(aq) H = 27 kJ
H2O(l)  Ca(OH)2(s) H = -65.2 kJ
*
*Endothermic : H is positive; heat is on the reactants
side of the equation (Heat absorbed)
*NH4NO3(s)  NH4+(aq) + NO3-(aq) H = 27 kJ
*NH4NO3(s) + Heat  NH4+(aq) + NO3-(aq)
*NH4NO3(s) + 27kJ  NH4+(aq) + NO3-(aq)
*
*Exothermic : H is negative; heat is on the
products side of the equation (Heat released)
*CaO(s) +
*CaO(s) +
*CaO(s) +
H2O(l)  Ca(OH)2(s) H = -65.2 kJ
H2O(l)  Ca(OH)2(s) + Heat
H2O(l)  Ca(OH)2(s) + 65.2 kJ
*
*Heat of combustion is the enthalpy change for the
complete burning of one mole of the substance
*CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) H = -891kJ
*CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) + Heat
*CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) + 891kJ
*
A hot piece of metal (at 155°C) with a mass of 4.68g is
placed into 53.9 grams of water at 22°C. The water
(Cs = 4.184 J/g°C) heats up to 37.1°C. What is the
specific heat of the metal?
*
How much heat is released by the combustion of
250.0 g of octane, C8H18?
Octane ΔHcomb = -5471 kJ/mol