topic 8

Question 1

recall the standard conditions

Answer 1

100 kPa
298K

Question 2

what sources of error could there be in enthalpy change experiments

Answer 2

improper placement of the thermometer bulb
not enough thermometer reading
spillage
unwanted heat loss to the surroundings
errors in temperature and mass measurement
incomplete combustion/reaction

Question 3

what is meant by the term bond enthalpy

Answer 3

the energy required to break a covalent bond in an atom in one mole of atoms in the gaseous state

Question 4

what is meant by mean bond enthalpy

Answer 4

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

Question 5

what is the limitations of using mean bond enthalpies to calculate enthalpy change

Answer 5

these values are average values
the calculation is for gaseous species so the reactions that involve solids and liquids will be even less accurate
mean bond enthalpy data differs in different environments (different strengths in different environments)

Question 6

what are the economic benefits of using catalysts in industries

Answer 6

quicker and more efficient reaction
save energy costs

Question 7

how would you calculate enthalpy change of formation

Answer 7

sum of enthalpy change of products - sum of enthalpy change of reactants

Question 8

how would you calculate enthalpy change of combustion

Answer 8

sum of enthalpy change of reactants - sum of enthalpy change or products

Question 9

what is meant by an exothermic reaction

Answer 9

more energy is released when the bonds are formed in the products than is used to break the bonds in the reactants