The enthalpy change for a chemical reaction is always the same, regardless of the route from reactants to products
How can you reduce uncertainty in mass measurements (weighing by difference)?
Use a balance with a greater resolution, use a larger mass
What is percentage uncertainty and how do you calculate it?
100 x absolute uncertainty/calculated value
How do you calculate enthalpy change experimentally?
q=mcΔt
Where m = mass of solution that changes temp. (1g=1cm^3), c=shc, Δt=temperature change measured using thermometer, q=heat energy taken in/released in J
Divide this number, in kJ, by the number of moles of the limiting reactant
Add a sign to show whether enthalpy change is exothermic or endothermic
Why may an experimental value for enthalpy change be different to the theoretical value?
Heat loss to apparatus/surroundings
Incomplete combustion
Non-standard conditions
Evaporation of alcohol/water
How do you prevent heat loss to surroundings/apparatus?
Insulate beaker by placing it in a polystyrene cup with a lid
Avoid large temperature differences between surroundings and calorimeter
Use a bomb calorimeter
Other than preventing heat loss, how can the accuracy of this experiment be improved?
Read thermometer at eye level to avoid parallax error
Stir solution so temperature is evenly distributed
Use digital thermometer for more accurate and faster readings
Use greater concentrations+masses, which leads to greater temp. change thus smaller uncertainty
