[starsnhearts89]

I know you're supposed to show your attempt at a problem before asking for general help but I don't know where to start with this! Could someone please show me some pointers or at least set me in the right direction on how to start and do these problems?

Use Hess’ Law to find the change in enthalpy for the following reaction:
3NO(g)  N2O(g) + NO2(g) ΔH = ?
Given:
1. 2NO(g) N2(g) + O2(g) ΔH = -180.7 kJ
2. 2NO2(g) 2NO(g) + O2(g) ΔH = 113.1 kJ
3. 2N2(g) + O2(g)  2N2O(g) ΔH = 163.2 kJ
ΔH = ?

&

25 mL of 1.50 M NaOH and 25 mL of 1.50M HCl are placed in a calorimeter; both are initially at 24.0oC. After stirring, the final temperature is 34.2oC. Calculate qsolution, qreaction and ΔHreaction (in kJ/mol). Assume the density of the solution is 1.00 g/mL and the specific heat of the solution is 4.18 J/goC. Pay close attention to the signs of these values.

[Jorriss]

Suppose you want to know the enthalpy of the reaction:
A -> C

But you're only told that:
A -> B has an enthalpy of X

and

B -> C has an enthalpy of Y.

If you add the reactions you get A + B -> B + C or, A -> C with a net enthalpy of X + Y.

This works because enthalpy is a state function meaning it is path independent so what you do is devise a set of steps of known enthalpy to find the enthalpy of the desired reaction.