Energetics Flashcards
Enthalpy change
4.1 Enthalpy change
The heat energy change measured under constant pressure whilst temperature depends on the average kinetic energy of the particles
Standard conditions
4.1 Enthalpy change
Pressure= 100kPa
Temperature= 298K
Standard enthalpy of formation
4.1 Enthalpy change
The enthalpy change when one mole of substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states
Standard enthalpy of combustion
4.1 Enthalpy change
The enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states
calculating enthalpy change
4.2 Calorimetry
q=m x c x T
Specific heat capacity
4.2 Calorimetry
The amount of heat needed to raise the temperature of 1g of substance by 1K, measured in joules per gram per kelvin
Calorimeter
4.2 Calorimetry
The apparatus used to measure the heat changes in chemical reactions
Hess’ Law
4.3 Applications of Hess’s law
The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products
Bond dissociation enthalpy
4.4 Bond enthalpies
The enthalpy change required to break a covalent bond with all species in the gaseous state
Mean bond enthalpy
4.4 Bond enthalpies
The average value of the bond dissociation enthalpy for a given type of bond taken from a range of different compounds
Required practical 2
Required practical 2
polystyrene cup
what reactions is this used practical for
Required practical 2
- acid + metal
- acid + metal carbonate
- displacement of metals
- neutralisation
what are the steps for the polystyrene cup practical
Required practical 2
1)put polystyrene cup in beaker
2) in cup put 25 cm cubed of acid using a measuring cylinder
3)put thermometer in acid and measure starting temp until min 4
4)put 5g of solid sample in acid on min 4 and stir
5)measure temperature every min for 10 min and record higherst temp reached
6) calculate change in temperature
7)repeat two more times and calculate a mean temp change, discarding any anonymily results
8)repeat for each sample
9)the sample with the highest temperature change is the most reactive metal.
what can you do to reduce heat loss
Required practical 2
put a lid on the polystyrene cup
exothermic reaction profiles
4.4 Bond enthalpies
reactants energy higher then products
