CHEMISTRY COMMUNITY

Delta H fusion = Hm (liquid) - Hm (solid) as mentioned in the book and in lecture. What does Hm stand for? Are we going to have to know how to solve for delta H fusion or for the other delta H phase changes?

Hm refers to the molar enthalpy of the solid or liquid. and yes, i think we need to know to use these delta H for phase change problems.

We may need to know how to solve for them in some cases but lots of questions about phase changes usually give them to us to calculate the overall heat change. Check out the textbook problems, they should show whether or not you need them.

Typically deltaH(fusion) and deltaH(vap) will be given to us since what we are usually solving for is initial/final temp or the enthalpy of the reaction. I believe it is more important that you know how to distinguish and apply all of the different values given to you than it is to calculate these specific values. However, it is still important for us to know how to calculate the values in case we were ever asked to.

Most questions give the overall heat change but you should know how to solve for it. Doing a lot of problems in the textbook will give you a clearer idea on whether you need to know how to solve for the overall heat change.