DF2-

What does Hess’ Law State

The enthalpy change for any reaction is independent of the intermediate stages as long as the initial and final conditions are the same for each route.

Equation for enthalpy cycle of combustion? & reactants

H1= H2 - H3

H2 =reactions

H3= products

(Same for reactants-equation)

Combustion products are always carbon dioxide and water, you add the molecules that are missing with the arrows (adding oxygen)

Remember that the - is already in the equation and any other signs of the reactants or products are added on

Equation for enthalpy change of formation?

H1= -H2 + H3

H2 = reactants

H3 = products

Splitting all of the reactants/products into their individual elements eg: N2H4 into N2 and 2H2

Remember that the - sign isn’t removed and that if my numbers value is negative it becomes positive

Key things to remember about enthalpy change of reaction?

the diatomic molecules are split into elements with the number of them in front of the element

What direction do arrows point in combustion? (& reactants)

Down

What direction do arrows point in formation?

Up