5.2.3 - Calorimetry Flashcards
What is calorimetry!?
Calorimetry is an experimental method, used to measure an enthalpy change
What three formulae do we use to measure 🔼H !?
. Q = m X c X 🔼T
(heat energy j) (mass of water)
. Moles = mass âž— RFM
. 🔼H(kj/ mol)= (-Q) ➗ moles
Remember to convert j into KJ !!!
What happens in an exothermic reaction ?!
. The reaction releases heat energy
. The heat energy is absorbed by the nearby water
. The temperature of the water increases
What are the two significant sources of error in a combustion calorimetry experiment?
- Heat loss - most of the heat energy dissipates into the air instead of the water.
- Incomplete combustion - this releases less heat energy than expected.
What happens in combustion calorimetry !?
. The simplest type of calorimetry involves combusting a fuel to heat up water.
An example of combustion calorimetry :
. To measure 🔼H for the combustion of the liquid fuel methanol you would combust some methanol using a burner underneath a can of water
What happens in solution calorimetry !?
. Sometimes the reaction you are measuring, happens dissolved in some water
. In this case, the reaction still releases, heat energy and the water still absorbs it, but it just happens that the reaction and the water are in the same place
An example of solution calorimetry:
. To measure 🔼H for the displacement reaction between magnesium(s) and copper sulphate(aq)
What are potential sources of error for solution calorimetry?
. As for combustion calorimetry, heat loss and incomplete reaction, are potential sources of error.
. Furthermore, the water being heated is no longer pure water, it has things dissolved in it. This means the specific heat capacity is no longer exactly the same
What happens in an endothermic reaction !?
. The reaction absorbs heat energy from the water, so the water cools down.
. This results in a negative temperature change for the water
. Endothermic reactions have a positive enthalpy change
