Calorimetry Heat of combustion Heat capacity Solution calorimetry Calibration factor Bomb calorimetry.

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Presentation transcript:

Calorimetry Heat of combustion Heat capacity Solution calorimetry Calibration factor Bomb calorimetry

Calorimetry Highly exothermic combustion reactions can generate electrical energy. So this energy is related to enthalpy change and calorimetry is involved in enthalpy change with energy contents of foods. Calorimetry is directly associated with measurement of heat changes during chemical reactions. You will need to know how to calculate how much fuel is needed to be burnt in order to raise the temperature of water by a certain amount.

Heat of Combustion We are considering directly thermochemical/exothermic reactions the enthalpy change shows us how much energy being produced by the reactant per mole hence the unit kJ/mol. And the amount of energy released when 1 mole of a substance burns in oxygen is called the molar heat of combustion.

Heat of Combustion Lets look at how to calculate the amount of energy being produced if we know the mass of the reactant and hence predict how much will evolve. Example: how much heat will be released when 5.00kg of methane is burnt in excess air?

Heat Capacity HEAT CAPACITY: the amount of energy required to raise the temperature of an object by 1 Kelvin/C° The specific heat capacity is the amount of heat energy required to raise the temperature of a given substance of 1g by 1 kelvin. Take note the amount of heat depends on the substance and its mass and also if it does not undergo any change from states.

Solution Calorimetry This process is involved with a solid substance being dissolved in water and energy is either being absorbed or released. The change in heat energy (absorbed/released) for this particular reaction is measured by 1 mole of solid substance being dissolved In water is called Molar heat of solution.

Calorimetry Calorimetry: measurement of heat flow. Calorimeter: apparatus that measures heat flow. Now we are going to look at some examples of heat capacity and specific heat using the following rule. (SO COPY THIS DOWN!!!) Heat energy = (spec heat) X (grams of substance) X ΔT (change in temperature) Units of measurement (J g -1 ° C -1 ) X g X ° C = J

Calibration Factor Exercise 13.4 Q 2,3,4

Bomb Calorimetry This is used for measuring ΔH in foods, fuels and other combustion reactions. This type of calorimeter is a method for measuring the amount of heat evolved when a substance of known mass undergoes combustion in excess oxygen of a sealed container. How is it measured? By the temperature rise in a known amount of water that surrounds the container. Now write the experimental steps for bomb calorimetry when applying this to food.