Question

For the reactions, H2(g)+Cl2(g)----->2HCl(g)+xKJ H2(g)+Cl2(g)----->2HCl(l)+yKJ Which one of the following statement is correct? A)x>y B)x<y C)x=y D)more data required

Answer 1

This is quite a difficult question in that we have to make assumptions: I think the answer is `B`

Explanation:

`H_2(g) + Cl_2(g) rarr 2HCl(g) +Delta_1`

`H_2(g) + Cl_2(g) rarr 2HCl(l) +Delta_2`

The difference between `Delta_1` and `Delta_2` is the process:

`2HCl(l) + Deltararr2HCl(g)`

Energy is used to boil the liquid. `Delta_2` as written should be larger than `Delta_1` (i.e. when the gas is condensed energy is released).

Note that the fact that exothermic reactions (and this one certainly is) are written as NEGATIVE, is a distractor. Here, because the energy is listed as a product (and not as a separate thermoodynamic property), we should be able to say that `Delta_2>Delta_1`. That is we get more energy out when the product is a liquid than when it is a gas.

Others may have a different take on this (and they certainly may have a better way of rationalizing the answer!).