1. practicals
1.1. calorimetry
1.1.1. A reaction takes place in a polystyrene cup with known masses of each component and is stirred and you record the temperature change using a thermometer.
1.1.1.1. pros
1.1.1.1.1. 1) heat generated is from solutions themselves so only has to be kept in the calorimeter.
1.1.1.1.2. 2) polystyrene cups are very good insulators
1.1.1.1.3. 3) they have a low heat capacity, so absorb very little heat.
1.1.1.2. cons
1.1.1.2.1. 1) possible innaccuracy when measuring mass and temp
1.1.1.2.2. 2) solution is assumed to be pure water
1.1.1.2.3. 3) some heat is lost or gained from the surroundings. to limit the error a cooling curve can be drawn and the graph can be extrapilated to find a more accurate value
1.1.1.2.4. 4) some heat is absorbed by the cup
1.1.2. other forms of calorimetry
1.1.2.1. flame calorimeter
1.1.2.1.1. a flame is used to increase rate of reaction
1.1.2.2. bomb calorimeter
1.1.2.2.1. most accurate
1.1.2.2.2. a known mass of fuel is placed inside a steel container. the fuel is then ignited and heats the surrounding water.
2. elements in standard states
3. products
4. enthalpy
4.1. enthalpy change ∆H
4.1.1. The heat energy change at a constant pressure.
4.1.2. kJ mol –1
4.2. standard enthalpy of formation
4.2.1. The enthalpy change when one mole of that substance is formed from its elements in their standard states under standard conditions
4.3. standard enthalpy of combustion
4.3.1. The enthalpy change when one mole o a substance undergoes complete combustion under standard conditions. All reactants and products are in their standard states.
4.4. q=(-)mc∆T
4.4.1. energy required (J) = mass heated (g) ✖ specific heat capacity (4.18) ✖ temp rise (K) (C+273)
4.4.1.1. J=(g)(4.18)(K)
5. Hess' law
5.1. The enthalpy change for a chemical reaction depends only on the initial and final states and is independant of the path followed
5.2. formation ∆H = sum of ∆H formation of products - sum of ∆H formation of reactants
5.2.1. reactants
5.3. combustion ∆H = ∆H combustion of reactants - ∆H combustion of products
5.3.1. reactants