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# Do Now Thursday , January 09, 2014 - PowerPoint PPT Presentation

Do Now 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.

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Presentation Transcript

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

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

• 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?

• 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 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 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

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

Insulators

Conductors

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?

Q = mCDT

Q = mC(Tf – Ti)

Q = heat (joules-J)

m = mass (kg)

C = specific heat (J/kg °C)

DT = change in temp (°C)

• 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?

• 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.

• 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?

•  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?

• 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