1. Thermo Notes #3: Heat Equation
WCHS Chemistry

2. Heat & Energy Thinker Scenario: It’s a HOT, HOT summer day.
You get into your car....what do you NOT want to touch??
ANYTHING METAL!! Especially the metal buckles. WHY???
Is the metal buckle hotter than the rest of the car? Why does it burn you?
SAME TEMP AS REST OF CAR!
It’s a conductor (transfers thermal energy very easily)
You are at a lower temp than the seat belt
TE always moves from High temp → Low temp
TE moves quickly to your skin and BURNS!

3. Specific Heat Capacity
The amount of energy needed to increase the temperature of 1g of a substance by 1℃
Units = J/g℃ or Cal/g℃
Think of it like a “cost”
Every substance has their own “cost” to heat up!

4. Specific Heat Examples
Lead = J/g℃
Doesn’t need much energy to heat up
Doesn’t transfer much energy to water
Brass = J/g℃
(In the middle)
Aluminum = J/g℃
Needs a lot more energy to heat up
Transfers more energy to water

5. Question...
You are SUPER hungry, and you find a box of mac and cheese in your cupboard. What is holding you back from eating it right at that moment?

6. Specific Heat Examples
Lead = J/g℃
Brass = J/g℃
Aluminum = J/g℃
Water(liquid) = 4.18 J/g℃

7. Water(liquid) = 4.18 J/g℃ Specific Heat of Water
The amount of energy that it takes to heat up just 1 gram of water 1℃ is HUGE!!!

8. Would you go into a pool in March?
What about at night in the summer?

9. Q = mcΔT Heat Equation Q m c ΔT Symbol Definition Units
Quantity of Heat Energy
Joules (J) OR Calories (Cal) m
mass
Grams (g) c
Specific Heat Capacity
J/g℃ OR Cal/g℃ ΔT
| Change in Temp | ℃

10. Heat Equation Practice
How much heat energy is needed to raise the temperature of 425g of aluminum baking sheet from room temperature, 25℃, to a baking temperature of 200℃? (aluminum specific heat = J/g℃)
Q = mcΔT
Q = (425g)x(0.897J/g℃)x(175℃)
Q = 66, J

11. Heat Equation Practice
What is the specific heat of a substance that absorbs 2500 Joules of heat when a 1000g sample increases in temperature from 10.0℃ to 70.0℃?
Q = mcΔT
C = Q/mΔT
c = (2500J)/(1000g)x(60℃)
c = J/g℃

12. Heat Equation Practice
3. How much heat is released to your body when a cup of hot tea containing 200g of water is cooled from 65℃ to your body temperature which is 37℃?
Q = mcΔT
Q = (200g)x(4.18J/g℃)x(28℃)
Q = 23,408 J

13. Heat Equation Practice
4. Imagine you are working outdoors on a hot, humid day. If you drink four glasses of ice water at 0℃, how much heat energy is transferred to your body? Assume each glass contains 250g of water and that your body temperature is 37℃.
Q = mcΔT
Q = (1000g)x(4.18J/g℃)x(37℃)
Q = 154,660 J