1. Internal Energy
Liceo Alfano I
Lesson 5

2. Review Last week: Ideal gases Pressure vs. volume
Pressure vs. temperature
Volume vs. temperature
Two weeks ago: Heat propagation
Conduction, convection, radiation

3. Reminder Question What is thermal conductivity?
A quantity measured in degrees Celsius
How much energy it takes to increase the temperature of a material
Energy transfer due to a temperature difference
A measure of how well a material conducts heat

4. Reminder Question What is thermal conductivity?
A quantity measured in degrees Celsius
How much energy it takes to increase the temperature of a material
Energy transfer due to a temperature difference
A measure of how well a material conducts heat

5. Heating Different Materials
During the summer time, when you walk from the sand into the ocean, which is hotter?
Why could this be?

6. Sand vs. Water The sun transfers heat to the sand and water
What kind of heat propagation is this?
The sand and water each get the same amount of heat from the sun
Why does one get hotter than the other?
vs.

7. Heat Capacity
The sand and water are at different temperatures because they have different heat capacities
Heat capacity tells us how quickly a material’s temperature will increase for a given amount of heat transfer
Think of a pie: the crust and filling get the same amount of heat from the oven, but which part do you burn your mouth on?

8. Heat Capacity vs. Thermal Conductivity
Thermal conductivity = how well a material will conduct heat (heat passing, heat transfer)
Heat capacity = how quickly something will heat up (heat staying, temperature)
Heat going through the walls vs. temperature of the walls
vs.

9. Heat Capacity vs. Thermal Conductivity Practice
Are each of these examples of heat capacity (1) or thermal conductivity (2)?
I make a pizza and the tomato sauce gets hotter than the cheese
I burn my mouth when I eat the pizza
A pot doesn’t feel hot if I use a glove to hold it
Gold increases its temperature more quickly than silver
Walking barefoot across the street feels hotter than walking on the sidewalk

10. Specific Heat Capacity
If we look at the heat capacity per mass, we call this specific heat capacity.
A high specific heat capacity means that something takes a long time to heat up, while a low specific heat capacity means something heats up quickly.
Water has an extremely high specific heat capacity, while metals do not.

11. Calculating Specific Heat Capacity
We have a formula that relates:
heat (Q)
mass (m)
specific heat capacity (c)
change in temperature (ΔT)
Q = m c ΔT

12. Concept Question Remember, Q = m c ΔT
If I increase the specific heat capacity, will it take more or less heat to increase the temperature by 1 degree?
More heat
Less heat

13. Concept Question Remember, Q = m c ΔT
If I increase the specific heat capacity, will it take more or less heat to increase the temperature by 1 degree?
More heat
Less heat

14. Concept Question Remember, Q = m c ΔT
Remember the beach question. Does sand or water have a higher specific heat capacity?
Sand
Water

15. Concept Question Remember, Q = m c ΔT
Remember the beach question. Does sand or water have a higher specific heat capacity?
Sand
Water

16. Specific heat capacity/global warming
Video
Specific heat capacity/global warming

17. Specific Heat Capacity of Water
The specific heat capacity of a material is usually not a constant - it changes with temperature.
However, we generally only work around 15 deg. C, so we take the specific heat capacity of water as 1 C/g, or J/g.

18. Internal Energy Remember, heat is a kind of ENERGY
When you add heat energy to an object, where does that energy go?
The energy is used to increase the temperature, and it is stored in the object
Since it is stored in the object, we refer to this energy as internal energy
Change in internal energy = heat added to the object
ΔU = Q

19. Practice Problems Remember, Q = m c ΔT
How much heat is absorbed when 500. g of water , c = J/goC, goes from 25.0oC to 35.0oC?
What is the change in internal energy when 500. g of copper, c = J/goC ,  goes from 25.0oC to 35.0oC?
I have a cup filled with 0.150kg of coffee (c=4187J/kg°C) at 70°C. I add 0.01kg of milk (c=3800J/(kg°C)) at 5.0°C. What is the final temperature of the coffee and milk mixture?
I made a bowl of minestrone soup (c=4187J/kg°C). I then put 0.6kg of soup at 90°C in a 0.2kg glass bowl (c=840J/kg°C) that is initially at 20°C, what will be the temperature of the soup and the bowl when they have reached equilibrium?