Energetics

Question 1

enthalpy change definition

Answer 1

heat energy change under standard conditions

Question 2

difference between complete and incomplete combustion in terms of energy

Answer 2

incomplete combustion is less exothermic

Question 3

why can’t the hydration of a salt be used to measure enthalpy change easily

Answer 3

can’t measure exact volume of water, not easy to measure temperature change of a solid

Question 4

enthalpy change of formation eqn

Answer 4

enthalpy change of reaction= formation of products- formation of reactants

Question 5

enthalpy of combustion hess’ law eqn.

Answer 5

enthalpy change of reaction= enthalpy of reactants- enthalpy of products

Question 6

mean bond energies meaning

Answer 6

enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules

ONLY when atoms start and end in the gaseous state

Question 7

enthalpy change eqn

Answer 7

bond energies broken- bond energies made

Question 8

why must you stir the solution when calculating enthalpy change experiment

Answer 8

so all the solution is the same temperature

Question 9

what is a problem if the RoR is too slow for enthalpy change experiment

Answer 9

reaction occurs simultaneously with cooling

Question 10

errors in enthaloy change experiment

Answer 10

energy transfer from surroundings (usually loss)

approximation in specific heat capacity of solution. (assumes all
solutions have the heat capacity of water).

neglecting the specific heat capacity of the calorimeter- we ignore any
energy absorbed by the apparatus.

reaction or dissolving may be incomplete or slow.

density of solution is taken to be the same as water

Question 11

errors in calorimetry experiment

Answer 11

Energy losses from calorimeter * Incomplete combustion of fuel * Incomplete transfer of energy
* Evaporation of fuel after weighing
* Heat capacity of calorimeter not included
* Measurements not carried out under standard conditions as
H2O is gas, not liquid, in this experiment