# Which reaction will have a negative ∆H value

1. Jul 4, 2016

### TT0

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
Negative ∆H means that the product is more stable. Change from solid to gas requires energy so cancel out A and C. Reaction D doesn't make sense. The products of reaction B and E are more stable than the reactant because there is a full shell so it seems to me both would have a ∆H value. Can someone tell me what am I missing?

Cheers!

2. Jul 4, 2016

### Staff: Mentor

Reaction D does make a perfect sense.

Ionization always requires energy.

3. Jul 4, 2016

### TT0

I thought chlorine didn't monatomic gases. So are you saying D is the answer? If so, why does it release energy?

Thanks a lot

4. Jul 4, 2016

### Staff: Mentor

Every diatomic molecule can be split (forced to dissociation) at temperatures high enough. It typically requires a lot of energy (hence the need for high temperatures).

5. Jul 4, 2016

### TT0

I see, so D has a positive ∆H value.

Would you say both B and E have negative ∆H as the products are more stable?

Cheers!

6. Jul 4, 2016

7. Jul 4, 2016

### TT0

So I guess A is the answer then? As it does not ionise. C is sublimation which requires energy. If A is the answer, isn't energy required for a particle to turn into a gas?

Thanks!

8. Jul 4, 2016

### Staff: Mentor

E is not ionization.

9. Jul 4, 2016

### TT0

I see. I got confused and forgot ionisation does not mean turning into an ion. Thanks a lot