Paper 3: Required practical 2 - Measuring enthalpy change
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How can you reduce the uncertainty in the mass measurement?
• Use a balance with a greater resolution • Use a larger mass
How do you calculate enthalpy change of reaction experimentally?
• q=mcΔT • Convert to J, divide by the number of moles of the limiting reactant • Add a sign to show whether it 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 the 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 thethermometer at eye level to avoid parallax errors • Stir the solution so the temperature is evenly distributed • Use a digital thermometer for more accurate and faster readings • Use greater concentrations and masses, leading to a greater temperature change and thus smaller uncertainty