Calorimetry

Bomb calorimeter

A bomb calorimeter allows for the determination of the heat of reactions. Heat of reaction is the energy gained or lost during a chem reaction. Heat of combustion is the heat gained or lost during the combustion reactions.

Calorimeter

A device used to measure the heat absorb or evolved during a physical or chem change.

Example 2

A sample of methane with a mass of 0.3202 is burned is a bomb calorimeter with a mass of 2.000 kg and its specific heat is 2.45 j/gK. If the temp increases by 3.629 during the reaction, what is the heat of combustion fro the reaction. 2.000 kg = 2000 g 200x 2.45x3.629 = 17800 J = 17.8 kJ

Calorie

A unit of energy equal to 4.18 J.

Example

An iron ball has a mass of 125 g, initial temp of 25 C, and is heated to a temp of 45 C. The Cp is 0.450, so how much heat is absorbed? Triangle T = 45-25 = 20 q = 125x.450x20 = 1125 J (Round up to 1130)

Calorimetric calculations

Calorimetric calc: 1.Calc mass of solution 2. Calc the temp change of the solution 3.Calc the energy of the reaction. First law of thermodynamics: -qmetal = qwater Formula for heat gained/lost: q = cmTriangleT, or from the original equation: Combining: -c underscore m x m underscore m x TriangleT underscore m = c underscore w x m underscore w x TriangleT underscore w underscore m and w are the two substances. ex. c underscore metal = -c underscore water x m underscore water x TriangleT underscore water/m underscore metal x TriangleT underscore metal

Heat capacity

The quantity of heat needed to raise the temp of a given sample of a substance by 1 degree Celsius (Kelvin) Units: J/C, J/K, cal/C, cal/K

Specific heat capacity(Cp)

The quantity of heat required to raise the temp of 1 gram of a substance by 1 degree Celsius(Kelvin) at constant pressure. Is an intensive property. Dependent on temp, especially for gases. Is related to intermolecular forces. The higher the specific heat of a substance, the more energy is needed to raise the temp of the substance. Units: J/gxC, J/gxK, cal/gxC, cal/gxK

Calorimetry

The use of a calorimeter to measure the energy given off or absorbed during a physical or chem process. Calorimetry is used to determine the energy content of foods.

Equation of heat gain/loss

q = heat gained or lost = joules m - mass = grams Cp = specific heat = Joules/gC triangleT = change in temp = C q = mCpTriangleT