Standard enthalpy change of formation and Hess's Law

Question 1

what is the standard enthalpy change of formation?

Answer 1

the enthalpy change measured at 100kPa and a specific temperature, usually 298K, when one mole of a substance is formed from its elements in their standard states.

Question 2

what is Hess’ Law

Answer 2

Hess’s Law states that the enthalpy change of a reaction is independent of the path taken in converting reactants into products, provided the initial and final conditions are identical.

Question 3

the standard state of an element is the form in which it exists at the

Answer 3

specified temperature, usually 298K and a pressure of 100kPa

Question 4

the equation which shows the standard enthalpy change of formation of gaseous carbon dioxide is

Answer 4

C(s, graphite) + O2(g) = CO2(g)

Question 5

the equation which shows the standard enthalpy change for the formation of liquid ethanol is

Answer 5

2C(s, graphite) + 3H2(g) + 1/2 O2(g) = C2H5OH(l)

Question 6

most standard enthalpy changes of formation are

Answer 6

impossible to determine experimentally

Question 7

in general terms, the enthalpy cycle which is used to calculate enthalpy change of formation of a compound from the relevant enthalpy changes of combustion is:

Answer 7

ΔfH
component elements → compound
→ →
sum of ΔcH of elements sum of ΔcH of compound
combustion products