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Do Now Thursday , January 09, 2014PowerPoint Presentation

Do Now Thursday , January 09, 2014

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Thursday, January 09, 2014

- You heat a balloon filled with air. What happens to the pressure inside of the balloon? Why?

3.5 minutes

Do Now Check

- By the end of the day today, IWBAT…
- Explain and calculate specific heat

Why it matters in LIFE: Explains why certain objects are made out of certain materials

Why it matters in THIS CLASS: This is the last topic we are covering before spring break – you will have a mastery quiz on Monday so let’s hit 85%!

Thursday, 01/09/14

Thermometer Lab Wrap Up

- What were the two systems you dealt with in this lab?
- Which system is transferring energy into the water? How do you know?
- After you turned the hot plate on, what happened to the molecules on the surface of the plate?
- What type of energy is being transferred from the hot plate to the water?
- How does this transfer of energy affect the molecules of water?
- How does this transfer of energy affect the molecules of the liquid inside the thermometer?
- As particles of water strike the thermometer and transfer their energy into the liquid inside, what happens to the pressure of the thermometer’s liquid?
- How does this change in pressure allow us to use a thermometer to measure the temperature of a system?

Specific Heat

- In the last step of your lab, you calculated the total heat that was put into your system in order to raise the temperature of the water
- In order to be able to do this, you needed to know the SPECIFIC HEAT of the water

Specific Heat

- Specific heat is a property of matter that describes the amount of energy required to raise the temperature of one gram of a substance by 1 °C

Specific Heat

- Specific heat is a constant that relates heat and temperature change per kilogram
- Different materials have a different specific heat
- A low specific heat means heat is conducted through an object quickly

Specific Heat

CONDUCTORS: change heat easily

Low Specific Heat

Require little energy to change temp

INSULATORS: Do NOT change heat easily

High Specific Heat

Require LOTS of energy to change temp

Recall the “Fire Proof Balloon”Specific Heat Demonstration

- We have two balloons – one filled with water and one filled with air

Based on what you learned yesterday about temperature and pressure, what actually happens to the balloon?

Specific Heat – Equation

Q = mCDT

Q = mC(Tf – Ti)

Q = heat (joules-J)

m = mass (kg)

C = specific heat (J/kg °C)

DT = change in temp (°C)

Specific Heat Demo

- Why did the balloon filled with water not explode?
- The water balloon does not explode because the water inside absorbs the heat better than the air does
- Water has a HIGHER specific heat, which means it has a HIGH heat capacity
- It takes a lot more energy to change the temperature of the water than it does for the air

Practice Problem - Q = mCDT

- If the specific heat of methanol is 251 J/kg˚C, how many Joules of heat are needed to raise the temp of .250 kg of methanol from 18˚C to 33˚C?

Group Practice

- A .625 sample of water was cooled from 50˚C to 10˚C. How much heat was lost? The specific heat of water is 4,184 J/kg˚C.

Group Practice

- The heat capacity of lead is 130 J/kg˚C. How much heat (in J) is required to raise the temperature of 15 g of lead from 22˚C to 37˚C?

Group Practice

- What is the specific heat of a substance that absorbs 250 J of heat when a sample of 10 kg of the substance increases in temperature from 10˚C to 70˚C?

Exit Ticket

- Complete the exit ticket questions INDEPENDENTLY
- You are not getting enough INDIVIDUAL practice before assessments, which is one of the reasons why the grades are so low
- You don’t really know it unless you can do it ON YOUR OWN

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