Energetics Flashcards
Do endothermic reactions make or break bonds and do they release or absorb heat?
Break bonds which absorbs heat (energy)
Do exothermic reactions make or break bonds and do they release or absorb heat?
Make bonds which releases heat (energy)
Which reaction type absorbs energy?
Endothermic reactions
Which reaction type releases energy?
Exothermic reactions
Which reaction type makes bonds?
Exothermic reactions
Which reaction type breaks bonds?
Endothermic reactions
Give 2 examples of exothermic reactions
Combustion and Neutralisation
Give an example of endothermic reactions
Thermal decomposition
What is the difference between heat and temperature?
Heat - a measure of thermal energy
Temperature - a measure of how hot something is
Why is using standard enthalpy of formation/combustion a more accurate method to using mean bond enthalpy data?
Because standard enthalpy applies to individual molecules whereas bond enthalpies are a mean value for the same bond across different molecules which is less accurate
A bomb calorimeter can be used for accurate determination of the heat change during combustion of a fuel. A bomb calorimeter is a container of fixed volume that withstands the change in pressure during the reaction. The fuel is mixed with pure oxygen in the calorimeter, ignited and the temperature change is recorded. State why the heat change calculated from the bomb calorimeter experiment is not an enthalpy change.
Pressure not constant in bomb calorimeter and enthalpy change requires constant pressure
Suggest one change to the calorimetry experiment aside from preventing heat loss that decreases the percentage uncertainty while using the same thermometer
Use bigger mass of fuel so deltaT greater Allow more / greater volume of fuel
How would you calculate the percentage uncertainty of a thermometer that was used to measure temperature change?
= 100 x (Smallest possible increment x 2 divided by Change in temperature)
