energetics

Question 1

Equation for enthalpy change when using formation data

Answer 1

H= products- reactants

Question 2

Equation for enthalpy change when using combustion data

Answer 2

H= reactants - products

Question 3

In the enthalpy change equation what does the n stand for?

Answer 3

N is the amount in moles that is reacted. The reactant that is not in excess is used so calculate moles of both reactants

Question 4

In the enthalpy change equation what does the m stand for?

Answer 4

The mass of the solution in the cup. The one that was there before you added the second substance

Question 5

What are the two main sources of error in calculating enthalpy change of combustion?

Answer 5

Heat loss to surroundings

Incomplete combustion of fuel

Question 6

Is breaking bonds endothermic or exothermic?

Answer 6

Endothermic as energy is required to break bonds

Question 7

Is making new bonds exothermic or endothermic?

Answer 7

Exothermic as forming new bonds releases energy

Question 8

Equation for enthalpy change using bond data

Answer 8

H= bonds broken- bonds formed

Question 9

Why are bond values referred to as averages?

Answer 9

The actual value for each bond changes according to the structure of the rest of the molecule so an average across all molecules is calculated