Chem: 3.3 & 3.4

Thermochemical equation

A balanced chemical equation that includes the enthalpy change (heat) associated with the reaction, showing the amount of energy released or absorbed.

Specific heat capacity

The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius, varying according to the substance.

Lower specific heat capacity

indicates that a substance requires less heat to increase its temperature by one degree Celsius compared to other substances.

Higher specific heat capacity

indicates that a substance requires more heat energy to increase it temperature by one degree celsius compared to other substances

formula for specific heat capacity

q = mCAT

what is q = mCAT used for

calculating heat energy changes in a substance based on its mass, specific heat, and temperature change. heat energy absorbed or released during a temp change.

heat of combustion

heat energy released when a specified amount of the substance burns completely and is a positive value,

heat of combusiton equation

HC = q (kJ)/n

assumptions that need to be made about Hc calculations

complete combustion, no heat loss to surroundings, specific heat capacity is the same, no heat is absorbed by the beaker.

energy content

the amount of energy released per unit mass or volume of a food during combustion.

energy content formula

Energy content = q (kJ) / mass change (g)

calorimeter

device used to measure the heat energy absorbed/released by a chemical reaction, designed to minimise heat loss to the environment.

2 types of calorimeter

solution and bomb

solution calorimeter

A type of calorimeter that measures heat changes in a solution during a chemical reaction, typically under constant pressure.

bomb calorimeter

A type of calorimeter that measures the heat released during a combustion reaction in a rigid, sealed container, usually at constant volume. involves gases.

what is calibration factor (CF)

the energy rewuired to change the temp of the water by 1 degree for the particular calorimeter.

how to make more accurate measurement of heat energy

determine the calibration factor (CF)

Calibration factor formula:

CF = E/ delta T (TEMP CHANGE)

electric calibration

the process of verifying and adjusting electrical measuring instruments to ensure their readings are accurate and reliable

how is electric calibration done

use an electric heater to release a known quantity of heat energy and measure the rise in temperature of the water

chemical calibration

Use a chemical reaction that releases a known amount of thermal energy and measure the resulting rise in temperature of the water.

what is the calibration factor (CF) used for:

used to determine the energy (E) that is responsible for the temp. change that occurs during the reaction.

what is the benefit of the CF

more accurate way of measuring change in enthalpy, and once is found means we do not have to use q=mCAT

what are temeprature time graphs

show how a substance's temperature (y-axis) changes over time (x-axis) as heat is added or removed

well insulated calorimeter

easy to calculate temp change (from graph). substract start temp from final temp.

poorly insulated calorimeter

hard to calcualte temp change (form graph). must extrapolate backwards and draw a line of best fit.

what is energy efficiency

percentage of total energy in a substance that is converted into useful energy (work/heat), rather than being wasted