1. The problem statement, all variables and given/known data What is the total amount of heat required to heat a 0.2 kg of ice from a temperature of -20 degrees to a temperature of 30 degrees Celsius 2. Relevant equations Q=mcΔt Q=mLf Q=mLv 3. The attempt at a solution To solve this they break it down, almost like a chemical equation Qtotal= Q warm ice + Q Melt ice + Q Warm water (this is general equation) My understanding is that whenever we are dealing with heat transfer and the change in the state of an object(solid to liquid or liquid to gas) , we use Q=mLv (if its evaporating or condensing) or Q=mLf (if its freezing or melting) so keeping in mind Qtotal= Q warm ice + Q Melt ice + Q Warm water = m1c1Δt + mLf + m1c1Δt and then we continue to solve this.... and in another problem... the question says what mass of steam is produced when 2.4 X 10^6 J of heat is applied to 4kg of water at 20 degrees Celsius? For this one the general equation is according to the book Q total = Q warm water + Q boil (this is the general equation) Q total = m1c1Δt + mLf Now here is what bothers me......in question one...we start from ice, heat transfer occurs, which is represented by the latent heat equation mLf, and then the ice melts. In total there are 3 parts to the general equation... in other words form changes...what was in the form of ice, is now in the form of water... the same thing happens... in the second question..the form changes..from water..to steam...yet there are only 2 parts of the general equation there... Why? how? How can i learn to write these general equations? Is there a rule of thumb or something that can tell me how to structure these general equations...or how many parts to put in them?