I want to calculate the energy change when a solute is dissolved in water. I know that I can achieve this by using the equation $q=mc \Delta T$. My question is does the mass ($m$) change with the amount of solute added to the solvent?
For example, if I had 25g of water ($c=4.18$) as my solvent and 5g of sodium chloride as my solute. Would the energy change equal:
$$q=25 \cdot 4.18 \cdot \Delta T$$ or $$q=(25+5) \cdot 4.18 \cdot \Delta T$$