October 22 Objective To represent the changes of energy that occur

while a substance is being heated.

Do now! How much heat is needed to completely

melt 10 g of ice at 0 0 C ?

How much heat is needed to vaporize 10 g of water at 100 0 C ?

Calorimetry problems- review questions7. 2 (172 J/g)8. 4 (53,800J)

13. 1.2 C14. 50.1 kJ15. 226.0 kJ16. 2260. J17. 1380 J/g

States of Matter

States of Matter.

Energy Changes Associated with Changes of State

The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other.

The temperature of the substance does not change during a phase change !!!

October 23Objective: How to calculate heat from heating curvesDo now: Draw a heating curve for the heating of 2 grams of substance that are being heated at a rate of 50 J/min.Melting Point 20 CBoiling Point 80 C Substance begins to melt at minute 2 and melts for 1 minute.It begins to boil at minute 8 and it takes 3 minutes to completely boil.

Set 2 – Heat Answers 13 3 14 4 15 4 16 3 17 3 18 2 19 2 20 3 21 122J/g x 7.5 g= 915 J

MC answers1) 22) 13) 24) 35) 46) 37) 18) 49) 4

10) 4 * more about this topic next week

11) 412) 413) 314) 215) 1

Heating curve1) 20 C2) B and d 3) KE (temperature)

remains constant PE increases 3) S and L 4) 20 C 5) 60 C 6) GasT 7) Increases (is T!)

8) E9)20minx100J/min=2000J

2000J/20 g = 100J/g10)1000J/20 g = 50 J/g11)60 C

Types of energy

POTENTIAL ENERGY : STORED ENERGY. The energy

inside the substance. KINETIC ENERGY : Associated with

motion. Average KE = TEMPERATURE

If the substance is melting or boiling, heat is being absorbed, and is being used to change the state of matter.

THE AVERAGE KINETIC ENERGY DOES NOT CHANGE!!! THE POTENTIAL ENERGY INCREASES.

Endothermic Phase Changes

Melting Point and Freezing Point The temperature at which a substance

melts. Is the same temperature at which the substance freeze.

Boiling Point and Condensation Point are the same temperature.

Normal boiling point is the temperature at which a liquid boils at normal pressure.

Exothermic changes If the substance is undergoing

condensation or freezing then heat energy is being released. The potential energy is decreasing and the TEMPERATURE REMAINS CONSTANT!!!

VAPORIZATION IS ENDOTHERMIC In hot climates drinking water is cooled by

evaporating water from the surfaces of porous clay pots. As water evaporates it ABSORBS heat from the water inside the container which is maintained cool.

Like cooling yourself off on a hot day by pouring water over your body. As water evaporates it absorbs heat

FREEZING IS EXOTHERMIC In freezing weather, citrus crops are

sprayed with water to protect the fruit from frost damage. As the water freezes (around the fruit-outside the fruit!) it releases heat, which helps to prevent the fruit from freezing.

October 23 How to calculate the amount of heat that a

substance absorbs while it is being heated up. DO NOW 1 .-Calculate the amount of heat needed to

increase the temperature of 200g of water from 0 0C to 100 0C. The heating rate is 100J/min.

2.-How much heat is needed to completely vaporize 200 g of water at 100 0C

q (amount of heat ) table T

q = m C T

Heat of Fusion Hfus

Amount of heat needed to completely melt 1 gram of substance at its melting point.

At the melting point the heat is calculatedHeat = mass x Hfus

Heat of VaporizationAmount of heat needed to completely boil

off 1 gram of substance at its boiling point.

At the boiling point the heat is calculatedHeat = mass x Hvap

Describe what happens with PE and KE as phase changes

Identify MP and BP from heating curve MP=FP and PB=condensation point Define heat of fusion and heat of

vaporization Calculate the Hfus and Hvap from the heating

curves Cooling curves