Hess's law!?

Question

Given the following data:
TiBr2(s) + SnCl4(l) → SnBr2(s) + TiCl4(l) ΔH = -74 kJ
SnCl2(s) + Cl2(g) → SnCl4(l) ΔH = -195 kJ
SnBr2(s) + TiCl2(s) → SnCl2(s) + TiBr2(s) ΔH = -4.2 kJ

Find the ΔH of the following reaction:
TiCl2(s) + Cl2(g) → TiCl4(l)

Answer 1

ok the person before had the right answer but in case u were asked for working or u just want to know (u know for the tests and peace of mind) how it's done, my explanation is below. it's not really that hard once u get over the feeling of being overwhelmed.

so you see ure final equation. TiCl2(s) MUST be on the left side right? which one of the 3 equations has TiCl2(s)? The 3rd one. It's already on the left side so this equation will be ure guide. the ΔH stays the same since there is no change.

In the 3rd equation you can see that SnBr2 is not in the final one. You have to cancel it out. Which equation has SnBr2? Equation 1. Once again it is nicely located on the opposite side, meaning you don't have to change the negative sign. The delta H stays the same. You can also notice that TiBr2 gets cancelled as well.

Now the problem is SnCl4. It's not in the final equation so it must be cancelled out as well. Which equation has it? The 2nd one. So you cancelled it out. At the same time SnCl2 is cancelled coz it's on the left side of he 2nd equation and the right side of the 3rd.

So what you are left with now is the final equation. You add up the numbers. This was not really a good example to show the manipulation needed. Sometimes you have to reverse the equation in which case you need to make the sign opposite. Or multiply the coefficents to find the one you need. Hope that helps.

Answer 2

Answer is -74-195-4.2 = -273.2 kJ

Answer 3

erm....

sos i REALLY can't help!
but if you know the answer
(or anyone does) BRAVO!
genious! lol xx