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Do Now: Hand in specific heat lab & answer the following question on “do now” sheet:. 56 grams of hot copper are added to 140 grams of water in a 92 g aluminum calorimeter causing the temperature of the water to rise from 22.0 o C to 29.5 o C. What was the initial temperature of the hot copper?

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do now hand in specific heat lab answer the following question on do now sheet
Do Now: Hand in specific heat lab &answer the following question on “do now” sheet:

56 grams of hot copper are added to 140 grams of water in a 92 g aluminum calorimeter causing the temperature of the water to rise from 22.0oC to 29.5oC. What was the initial temperature of the hot copper?

Cwater=4180 J/(kg K) cAl=897 J/(kg K) cCu=385 J/(kg K)

slide2

Q1=mcDT

=(0.14kg)(4180 J/kg/oC)(7.5oC)=4389 J

Q2=mcDT

=(0.092kg)(897 J/kg/oC)(7.5oC)=619 J

Q3=mcDT

=(0.056kg)(385 J/kg/oC)(DTcu)

Q1+Q2+Q3=0

(4389 J) + (619 J) + [(21.56 J/oC)(DTcu) = 0

DTcu= - (4389 J + 619 J) / (21.56 J/oC) = -232 oC

DT = Tf – Ti Ti = Tf – DT = 29.5oC – (-232oC)

Ti = 262oC

56 g Cu

Ti=?

29.5oC

22.0oC

92 g Al

140 g water

agenda 3 5 2014
Agenda 3.5.2014
  • Describe states of matter
  • Explore what happens when a substance changes from one state of matter to another.
  • Label and explain “heating curves”
  • Use heat of vaporization and heat of fusion to calculate energy absorbed or released when a substance undergoes a change of state.
slide4

State of matter with fixed volume and shape. Molecules are in motion but are tightly packed and maintain their locations relative to neighboring molecules.

  • Solid
  • Liquid
  • Gas
  • Plasma
measure of the average kinetic energy per randomly wiggling particle
Measure of the average kinetic energy per randomly wiggling particle
  • Heat
  • Thermal Energy
  • Temperature
  • Specific Heat
slide6

Measure of the total amount of kinetic energy associated with the random motion of particles plus the total potential energy associated with the intermolecular bonds

  • Heat
  • Thermal Energy
  • Temperature
  • Specific Heat
slide7

State of matter that takes on the shape of its container but has a constant volume. Although molecules are tightly packed bonds are continuously changing as they change their locations relative to neighboring molecules.

  • Solid
  • Liquid
  • Gas
  • Plasma
slide8

In this state of matter molecules do not form lasting bonds with neighbors and spread out to occupy all the space available. With plenty of extra room between molecules this state of matter can be compressed into a smaller volume.

  • Solid
  • Liquid
  • Gas
  • Plasma
slide9

At high enough temperatures particles in a gas have enough kinetic energy to knock electrons free from neutral atoms resulting in this hot soup of charged ions.

  • Solid
  • Liquid
  • Gas
  • Plasma
slide11

Heat is added at a uniform rate to a pot of water that starts off at room temperature. The temperature of the water is shown for the first few minutes. Sketch what you think the rest of the graph look like if the pot is left on the stove for 20 minutes

slide12

This is what the graph actually looks like. Take 3 minutes to discuss in small groups what is going on here. Would the formula Q=mcDT work for the entire 20 minutes? Why or why not?

why does boiling water stay at 100 o c when you continue to add heat
Why does boiling water stay at 100oC when you continue to add heat?
  • In liquid state molecules are “stuck” to neighbors by temporary bonds
  • Addition of heat at the boiling point “un-sticks” molecules from neighboring particles WITHOUT increasing kinetic energy.

BIG IDEA –

At the boiling point adding heat results in a change of state. As H2O changes from liquid to gas thermal energy increases but temperature stays the same!

phase diagrams
Phase diagrams

Water Dry Ice

heating curves
Heating curves
  • http://www.kentchemistry.com/links/Matter/HeatingCurve.htm

HEAT

heat of fusion hf
Heat of fusion (Hf)

Amount of heat required to melt 1 kg at the melting point

Heat required to melt something: Q=mHf

Heat required to freeze something: Q=m(-Hf)

Example: Adding 668 kJ to a block of ice at 0oC causes 2.0 kg to melt. What is the heat of fusion of ice?

Q=6.68x105 J m=2.0 kg Hf=Q/m=3.34x105 J/kg

heat of vaporization
Heat of vaporization

Amount of heat required to change 1 kg of liquid to a gas at the boiling point.

Heat required to vaporize something: Q=mHv

Heat required to condense something: Q=m(-Hv)

Example: The boiling point of ethanol is 78oC. How much heat must be added to 750 g of ethanol at 78oC to turn it into a gas?

Hv=846 kJ/kg m=0.75 kg Q=mHv= 635 kJ

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