You can use the value of the equilibrium constant to determine Δ G. If K is 1 then Δ G is 0, if K is greater than 1 then Δ G is negative, and if K is less than 1 then Δ G is positive. This is because Δ G = -RT ln K. Δ G can then be used to find Δ H, per my previous comment.

If you know the signs of the Gibbs' energy change and entropy change you could use Δ G = Δ H - T Δ S. For instance, if you know that the reaction is spontaneous (Δ G is negative) and the products have a lower entropy than the reactants (Δ S is negative), then you know that the reaction must be exothermic because Δ H must be negative.

I'm not familiar with Malathion but with liquids the situation is a little different. For two liquids to be miscible, i.e. for them to be able to mix together uniformly, they have to have similar polarities. Since water is a polar solvent, Malathion would also have to be polar for the two liquids to mix. If the two liquids are miscible, then the evaporation of some water wouldn't affect whether Malathion remains mixed with the remaining water.

Multiplying a reaction by -1 means that you reverse it; in other words, your reactants become your products and your products become your reactants. By reversing the second equation you then have 2 electrons in your reactants, so that when you add the reactions you start and end with the same number of electrons.