Aug ‘171 3.03 Solid-Liquid-Gas, Phase change

3.03 Phase Changes of Matter

Dr. Fred Omega GarcesChemistry 100Miramar College

Water crystal

Heating-Cooling Curve

Aug ‘172 3.03 Solid-Liquid-Gas, Phase change

Phases of Matter: Terminology

Energy is required for phasechanges to occur.

Solid-Liquid-GasTriangle

Aug ‘173 3.03 Solid-Liquid-Gas, Phase change

Heating Cooling CurveFrom Ice to Steam and Vice-versa

What is the energy needed to take 1g H2O at 0°C to 100°C ? 80 +100+ 540 =720cal

Stage1

Stage2

Stage3

Stage4

Stage5

Heat Addition

6.01 kJmol

540 calg

4.184 Jg °

1 calg o

40.7 kJmol

80 calg

1.84 Jg °

0.43 calg

2.09 Jg °

0.50 calg

Aug ‘174 3.03 Solid-Liquid-Gas, Phase change

Heating Cooling CurveFrom Ice to Steam and Vice-versa

What is the energy needed to take 1g H2O at 0°C to 100°C ?

80 +100+ 540 =720cal

Stage1

Stage2

Stage3

Stage4

Stage5

Units Stage1S.h.ice

Stage2Heatfusion

Stage3specificheat(s.h.)water

Stage4Heatvaporization

Stage5S.h.gas

cal/g 0.50cal/gK

80cal/g

1.0cal/gK

540cal/g

0.50cal/gK

Jg-1K-1 2.11J/gK

334J/g

4,18J/gK

2257J/g

2.08J/gK

calmol-1 9.01cal/molK

1441cal/molK

18.102cal/molK 9728cal/molK

9.01cal/molK

Jmol-1K-1 38.1J/molK

6.02kJ/molK

75.33J/molK

40.1kJ/mol

37.5J/molK

1 calg o

4.184 Jg °

540 calg

40.1 kJmol

80 calg

60.2 kJmol

Aug ‘175 3.03 Solid-Liquid-Gas, Phase change

At the molecular level:Molecules or matter is held together by “glue” called

intermolecular forces

Intermolecular Forces

Energy added (K.E. increases)

SOLID LIQUID GAS

Aug ‘176 3.03 Solid-Liquid-Gas, Phase change

Intramolecular Forces -Force which keeps molecule together,

i.e., bonds.

Intermolecular Forces -Attractive force between molecules.

Responsible for keeping matter in solid or liquid phase.

Keeping Matter together

Aug ‘177 3.03 Solid-Liquid-Gas, Phase change

Heating / Cooling CurvesFrom Steam to Ice and Vice-versa

.334 kJg

80 calg

2.26 kJg

540 calg

4.184 Jg °

1 calg o

540+100+80=720cal

2.09 Jg °

0.50 calg

1.84 Jg °

0.43 calg

What is the energy needed to take 1g H2O at 0°C to 100°C ?

Aug ‘178 3.03 Solid-Liquid-Gas, Phase change

SAMPLE PROBLEM 2.12Heat of Fusion

STEP 1 Given 26 g of H2O(s) Need joules to melt iceSOLUTION

Ice cubes at 0 °C with a mass of 26 g are added to your soft drink.a. How much heat (joules) must be added to melt all the ice at 0 °C?b. What happens to the temperature of your soft drink? Why?

b. The soft drink will be colder because heat from the soft drink is providing the energy to melt the ice.

STEP 2

STEP 4 Set Up Problem

STUDY CHECKIn a freezer, 150. g water at 0 °C is placed in an ice cube tray. How much heat, in kilojoules, must be removed to form ice cubes at 0 °C?

STEP 3 Equalities/Conversion Factors

Aug ‘179 3.03 Solid-Liquid-Gas, Phase change

SAMPLE PROBLEM 2.13Using Heat of Vaporization

In a sauna, 150 g of water is converted to steam at 100 °C. How many kilocalories of heat are needed?

STEP 1 Given 150 g of H2O(l) to H2O(g) Need kilocalories of heat to change stateSOLUTION

STEP 2

STEP 3 Equalities/Conversion Factors

STEP 4 Set Up Problem

STUDY CHECKWhen steam from a pan of boiling water reaches a cool window, it condenses. How much heat, in kilocalories (kcal), is released when 25 g of steam condenses at 100 °C?

Aug ‘1710 3.03 Solid-Liquid-Gas, Phase change

SAMPLE PROBLEM 2.76Combining Heat Calculations

2.76 A pitcher containing 0.75 L of water at 4°C is removed from the refrigerator. How many kilojoules (and Calories) are needed to warm the water to a room temperature of 22 °C

Stage1

Stage2

Stage3

Stage4

Stage5

Heat Addition

6.01 kJmol

540 calg4.184 J

g °

1 calg o

40.7 kJmol

80 calg

1.84 Jg °

0.43 calg

2.09 Jg °

0.50 calg

Aug ‘1711 3.03 Solid-Liquid-Gas, Phase change

SAMPLE PROBLEM 2.37Combining Heat Calculations

2.37 Calculate in Joules and calories the following:

a) Energy required to heat 25.0 g of water from 12.5°C to 25.7°C

b) Energy required to heat 38.0 g of copper from 122°C to 246°C

c) Energy lose when 15.0 g of ethanol cools from 60.5 °C to -42.0 °C

d) Energy lose when 112 g of iron cools from 60.5°C to -42°C

Aug ‘1712 3.03 Solid-Liquid-Gas, Phase change

SAMPLE PROBLEM 2.14Combining Heat Calculations

Using Table 2.13 and the specific heat of ethanol (2.46 J/g °C), calculate the total heat, in joules, needed to convert 15.0 g of ethanol at 25.0 °C to gas at 78.0 °C.

STEP 1 Given 15.0 g of ethanol at 25.0 °CNeed heat (J) needed to warm the ethanol and change it to gas

SOLUTION

STEP 2 When several changes occur, draw a diagram of heating and changes of state.

Total heat = joules needed to warm ethanol from 25.0 °C to 78.0 °C+ joules to change liquid to gas at 78.0 °C

Aug ‘1713 3.03 Solid-Liquid-Gas, Phase change

Vapor PressureEvaporation occurs when molecules have sufficient energy to escape the interface of a liquid substance.

Vapor Pressure - The pressure exerted by the liquid’s vapor at equilibrium.Normal Boiling Point - The temperature at which the vapor pressure of a liquid equals the atmospheric pressure.

Aug ‘1714 3.03 Solid-Liquid-Gas, Phase change

Phase Diagram (Revisited)Heating -Cooling Curves and their relation to the Phase Diagram

Aug ‘1715 3.03 Solid-Liquid-Gas, Phase change

SummaryThe equilibria between the three phase of a substance is a

function of the pressure and the temperature as shown in a

phase diagram. Equilibria between any two phase are

indicated by a line. The line through the melting point usually

slopes slightly to the right as pressure increases (solid is

more dense than liquid). For water this slope is to the left.

Features of the phase diagram is the normal melting point

(freezing point) and the normal boiling point. The triple point

is the condition in which all three phases of matter exist and

the critical point is the condition in which the liquid and the

gas phase are indistinguishable.