Chapter 2B - Calculating energy using specific heat capacity of water

• the amount of energy required to raise the temperature of 1.00g of substance by 1.00°C or 1.00K • increase in heat capacity = more effective storage of heat energy

• fuel sample combusted w/ O₂ for a period of time • heat released in exothermic reaction heats a known mass of water sitting above the sample Once reaction is stopped measure: • temperature change of the water • mass of fuel combusted • calculate the energy absorbed by the water • calculate the energy content of the fuel

• low accuracy: large amounts of heat loss to the surroundings & water container (up to 90% loss) • mass of water being heated will change throughout experiment due to evaporation • not all fuels/foods are available in a form that can be safely & feasibly combusted

• more accurate technique to estimate energy content of fuel/food

• insulated reaction vessel designed to minimise amount of heat lost by water to the surroundings

• used to measure the enthalpy change for reactions that occur in solution • reactions can be endothermic or exothermic

• well-insulated calorimeter still loses some heat • CF accounts for this heat loss • energy (J) required to raise the temperature of water in calorimeter by 1 degree

• Connect calorimeter containing the water to power supply • Turn power supply on & record voltage (V) in volts & current (I) in amps • After t seconds, turn power supply off & record change in temperature of water • Calculate energy (q) passed through the heating element of the calorimeter • Calculate the CF

• Conduct an exothermic reaction w/ known enthalpy change & known quantity of fuel • Measure temperature change of water • Use stochiometry to calculate theoretical amount of energy released by the reaction • Calculate the CF

• Calculate experiment using calibration calorimeter • Measure temperature change of water • Calculate energy released using q=CF X ΔT • Calculate the enthalpy change of the reaction Volume of water/reaction solution in the calorimeter should be the same during the calibration process and the chemical reaction

• little heat loss • temperature of contents decrease slowly

• temperature rise is less than in a well-insulated calorimeter • temperature of the contents decreases more rapidly

• poorly-insulated calorimeter: compensate for any heat loss • use adjusted ΔT value for CF calculations • leads to more accurate/reproducable results • more frequent temperature measurements produces more precise results