1. Unit 7: Thermochemistry Calculations Phase Change and q=mcΔT
Objectives
Calculate the energy of a phase change
List factors that affect how a substance heats up
Define Calorie
Apply formula q=mcΔT
Factor
Possible Units
Energy Heat (q)
Kilojoule (KJ) Joule (J) Calorie (Cal)
Amount of substance
Grams (g) Mole (mol)
Temperature
Kelvin (K) Celsius (◦C) (do not need to convert for ∆T)

2. Heat of Fusion and Vaporization
ΔHfus = Heat of fusion = Energy change in kilojoules/Mole when a substance freezes or melts. (Solid/Liquid)
ΔHvap = Heat of vaporization = Energy change in Kilojoules/Mole when a substance boils (vaporizes) or condenses. (Liquid/Gas)
The standard heat of fusion of water = 6.02KJ/Mole
This means it takes 6.02 KJ to change 1 mole of water into ice or 1 mole of ice into water. The sign depends on which way the question is asking.
Given that a box of chocolates costs $6.02/box how much would 3 boxes cost?
Given 3 moles of water are frozen to ice what is the energy change in KJ?

3. Factors for Heating.
The amount of heat (q) it takes to heat up a substance depends on a variety of factors. Determine which takes more energy for the following.
Two cups of water, cup 1 and cup2, everything is equal except cup 1 will be heated to 40 ◦ C and cup 2 will be heated to 80 ◦ C. Which takes more energy?
A cup of water and a bucket of water. Both are being heated to 40◦ C.
A beaker of water and a beaker of mineral oil. Both are being heated to 35 ◦ C
So what factors determine heating? What is the formula

4. Specific Heat capacity and calories
Different substances heat up differently. (due to their different chemistry)
The way a substance heats is given by a value called the specific heat capacity.
The specific heat capacity units are 𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑚𝑜𝑢𝑛𝑡 𝑥 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 or 𝐽𝑜𝑢𝑙𝑒𝑠 𝑔𝑟𝑎𝑚 ∘𝑐𝑒𝑙𝑠𝑖𝑢𝑠
The specific heat of water is 𝐽 𝑔∘𝐶 this means that 4.18 joules of energy can raise the temperature of 1 gram of water 1 degree Celsius.
Another unit of energy is called the calorie. 1 calorie = 4.18 joules.
If a snickers bar has 215 calories that is enough energy to raise the temperature of 10 grams of water by how much? (q=mcΔT)