PHYSICAL - ENERGETICS

Question 1

define calorimetry

Answer 1

quantitative study of chemical energy in a chemical reaction
- allows us to measure the amount of heat transferred into a particular mass of a substance

Question 2

calorimetry equation 1

Answer 2

q = mc(delta)T
q = energy in J
m = mass in g
delta T = change in temp in calvin or celsiued
c = specific heat capacity J/Kg-1

Question 3

calorimetry equation 2

Answer 3

DELTAH = q/n
deltaH = enthalpy change
q = energy in kJ
n = moles

Question 4

calorimetry general method

Answer 4

1. Washes the equipment (cup and pipettes etc) with the solutions to be used then dry the cup
2. Put polystyrene cup in a beaker for insulation and support
3. Measure out desired volumes of solutions with volumetric pipettes and transfer to insulated cup
4. Clamp thermometer into place thermometer bulb needs to be immersed in the solution
5. Measure the initial temperatures every minute for 2-3 minutes
6. At minute 3 transfer second reagent to cup.
7. Stirs mixture (ensures that all of the solution is at the same temperature)
8. Record temperature every minute after addition for several minutes

Question 5

errors with calorimetry method

Answer 5

• energy transfer from surroundings (usually loss)
• approximation in specific heat capacity of solution - assumes all solutions have the heat capacity of water
  reaction or dissolving may be incomplete or slow.

Question 6

bond enthalpy definition

Answer 6

enthalpy required to break 1 mole of covalent bond with all species in the gaseous state

Question 7

mean bond enthalpy definition

Answer 7

the mean enthalpy change when one mol covalent bond breaks averaged over a range of compounds

Question 8

enthalpy change

Answer 8

enthalpy change = bond breaking -bond making

Question 9

standard enthalpy change of formation definition

Answer 9

enthalpy change when one mol of a substance is formed from its elements under standard conditions (298K and 100kPa) and all reactants and products in standard states

Question 10

standard enthalpy change of formation equation

Answer 10

products - reactants = enthalpy change of reaction

Question 11

standard enthalpy change of combustion definition

Answer 11

enthalpy change when one mole of a substance is completely combusted in oxygen under standard conditions (100kPa and 298K) and all reactants and products in standard states

Question 12

standard enthalpy change of combustion equation

Answer 12

reactants - products = enthalpy change of reaction

Question 13

Hess Law

Answer 13

1st law of thermodynamics
- States that in a reaction the bond enthalpy change is independent of the route taken

Question 14

Hess Law equation

Answer 14

DELTAH1 = DELTAH2 + DELTAH3