CONCEPT: HEAT SUMMATION Many reactions are difficult, even ...

CONCEPT: HEAT SUMMATION Many reactions are difficult, even impossible, to carry out in a single chemical step. •

They may often times require multiple steps to get to the final products.

__________ Law  states that the enthalpy change (∆H) of an overall process is the sum of the enthalpy changes of its individual steps.

EXAMPLE: For the following example calculate the unknown ∆H from the given ∆H values of the other equations. Calculate the ∆Hrxn for S(s) +   3 O2 (g)

SO3 (g)

2

∆H = ?

Given the following set of reactions:

 

1 2

2

 

S (s) +   1 O2 (g) 2

SO3 (g)

 

1 2

SO2 (g)

2 SO2(g) + O2 (g)

∆H1 = – 296.8 kJ

∆H2 = 198.4 kJ