My teacher gave me 2 problems:

1. Calculate the heat of dissolution of MgCl2: solved for qRXN

2. Calculate the heat of combustion of C4H10O: solved for qcal

Why? Why am I solving for 2 different types of q when they are essentially the same problem?

For the 2nd problem, here is the background info: 7.00 mL of C4H10O (density = 0.714 g/mL) is burnt in a calorimeter (calorimeter heat capacity = 10.34 kJ/°C). The temperature in the calorimeter rises from 25.0 °C to 39.7 °C.

Then, it asks me to calculate q when 1 mole of C4H10O is burned.

Here's the process to solve for q: qreaction = (74g/mol)/5.00 g x (-152 kJ) = - 2.25 x 10 kJ/mol

I get where 5g, and -152 kJ comes from, and 74g/mol is the molar mass of C4H10O.

But why do I multiply these numbers together? Is it some kind of formula? And, if it asks me to calculate for when 1 mole is burned, then why do I have to do 74/5? Can't I just do 74g because that's 1 mole?

Sorry for the word vomit, I'm just so confused.