Kinetic and Potential Energy on the Nanoscale

Kinetic Energy on the Nanoscale

thermal energy

Baseball

Looking at a tiny piece

within the baseball.

Potential Energy on the Nanoscale

Case 1

Case 2

Different position means different potential energy

Temperature

Cool Block

Warm Block

Figure 3. Two blocks touching. One is initially warm and one is initially cool.

Temperature

measure of average kinetic energy of KMT particles

TemperatureFahrenheit

212oF

32oF

Celsius

100o

C

0oC

Kelvin

373K

273K

Figure 5. The three common temperature scales (Fahrenheit, Celsius, and Kelvin). The degree markings on thermometers are based on the freezing and boiling points of water (depicted here for each scale).

oF = (9/5 × oC) + 32oC = 5/9 × (oF – 32)

oF = (9/5 × oC) + 32oC = 5/9 × (oF – 32)

Temperature

Cool Block

Warm Block

Figure 3. Two blocks touching. One is initially warm and one is initially cool.

Energy is transferred from one block to the other – there is a heat flow, or heat is

transferred

Warming/Cooling (Transferring Heat)

• Do all substances change their temperature same way?

• Do all substances absorb same amount of heat to appear “hot”?

Warming/Cooling (Transferring Heat)

• For different amounts of a particular substance (iron for example), will the same amount of heat cause the substance to feel hot?

• Is the same amount of heat needed to cause the same temperature change for different masses (of same substance)?

Specific Heat Capacity

Amount of heat needed to raise the temp of 1 gram of

material by 1 oC

Using Heat Capacity

• Heat transferred = q = Cs * m * T

• Determine the amount of heat transferred for 15.0 g of water if the temperature changes from 20.0 oC to 50.0 oC.

Using Heat Capacity

• If the same amount of heat transferred to water in the last problem was transferred instead to a 15.0 g sample of iron that was at 20oC (specific heat capacity=0.449 J/g oC), what change would occur for the iron?

– Ans: The iron would increase its temperature by 281 oC.

Phase Changes

• If we continue to add heat to our water sample, what happens?

• Temp will continue to increase• When we reach 100 oC, what

happens?– Water boils

Phase ChangesDescription of Phase

Change Name of Change

Solid Liquid Melting or Fusion

Liquid Solid Freezing

Liquid Gas Vaporization

Gas Liq Condensation

Solid Gas (directly without changing to liquid first,

dry ice does this)

Sublimation

Gas Solid (directly without changing to liquid first)

Deposition

Ice Bath Activity

• Was there a temperature change?• Was there a flow of heat?• Was energy conserved? How can

there be a flow of heat, but no temperature change?

Phase Changes

temperature of substance undergoing phase change does

not change during the phase change

Latent Heat of Fusion

• Heat required to melt 1 gram of a material

333J/g for water (ice)

• How much heat would be needed to melt 20 g of ice?

Latent Heat of Vaporization

• Heat required to vaporize 1 gram of a material

2260 J/g for water (ice)

• How much heat would be needed to vaporize 20 g of ice?

Heat transfers

• One of two things may occur– Temperature change– Phase change– HANDLE EACH DIFFERENTLY!– Each may occur in stages or steps!

Changes with Heat

Amount of Heat Transferred

Te

mp

era

ture

(oC

)

Heating Ice

Heat transfers

• You may see one of two things occur– Temperature change– Phase change– HANDLE EACH DIFFERENTLY!– Each may occur in stages or steps!

General Heat Transfers

• If a 300 g sample of water were at 22.4 o C, what transfer of heat would occur to make all of this sample become ice?

• Note: for water Hvap = 2260 J/g; Hfus = 333 J/g

Cs (wtr) = 4.184 J/(g oC); Cs (ice) = 2.06 J/(g oC)

Applying our understanding of heat – including

conservation of energy• If a 10 g block of iron that was at 90o C was

added to an insulated container of water that was at 25o C, what would happen?

• Once the temperature of the water stopped rising, the water and the block were at 30o C. How much water was present?

• (Note the specific heat capacity of iron is 0.449 J/(g oC) and that for water is 4.184 J/(g oC).)

Water and Cold Objects Activity

• Was there a temperature change?• Was there a flow of heat? From

where to where?• If object is the system, was it an

endo- or an exothermic change?• Was it the same heat flow for each

object?

Water and Cold Objects Activity

Role of heat capacity!

NOW, ICE…..