How do you know which variables in an equation are constant? My solution: I think that variables in an equation with no [tex]\Delta[/tex] in front of it will be assumed that it is constant always. Is this correct for any equation? But for PV=nRT, it is kind of ambiguous. Should the problem should always tell you what is constant and what isn't? Like it the problem said the temperature changes, it must also say that either Pressure changes or Volume changes or what you need to solve for right?