This will happen if q is true. Here is a more intuitive way of doing this. To demonstrate that the argument is invalid, we need to come up with a counterexample, that is, an instance of statements p and q for which the premises are true, but the conclusion p is false. The earth is round. Decide whether the following argument is valid.
Heat dissipation accompanies every irreversible chemical reaction.
Therefore, if a chemical reaction is reversible, it dissipates no heat. In order to analyze the argument, we translate it into symbolic form. The first sentence then becomes p q. Thus we suspect that the argument is invalid, and we look for a counterexample. The only way for an implication to be false is for the antecedent to be true and the consequent to be false.