Science 10 – Hydrologic Cycle and Heat Capacity

Objectives Define specific heat capacity and use it to

calculate thermal energy Describe the hydrological cycle Distinguish between different phases of the

hydrological cycle Calculate heat of fusion and heat of

vaporization

70% of Earth’s surface is covered with water

Water plays a major role in the absorption and distribution of thermal energy, influencing both weather and climate: the great

moderator

Planet Water

Hydrological Cycle Water is constantly moving through the

biosphere Changing phases from solid to liquid to gas

and back again Uses evaporation, condensation,

transpiration, and precipitation Add or release thermal energy for phase

changes

How Oceans Effect Distribution of HeatLarge Reservoirs of Heat

1. Water has high specific heat capacity2. Water has low albedo, high absorption

(90% of incoming solar radiation is absorbed

Large Reservoirs of Heat 3. High heats of fusion and vaporization• 4. Water is a fluid and heat can be

distributed

Areas around large bodies of water (Great Lakes, oceans) do not experience extreme weather changes like areas that don’t have large bodies of water i.e continent interiors (think Saskatchewan and Alberta), and deserts.

It takes a lot of solar radiation to heat water, so water is a heat sink.

It absorbs a great deal of solar radiation, keeping the region cooler during the day, and it slowly reradiates the heat at night

Large bodies of water MODERATE temperature and climate.

Ocean Currents Large effect on weather in coastal

communities Influence worldwide climate

Gulf Stream

Surface current: starts in Caribbean and flows up the Eastern coastline of US and Canada up to British Isles. Also called North Atlantic Drift.

Huge air and ocean currents distribute heat in amazing patterns around the earth,

greatly affecting the climate and weather of many regions.

Phase Changes and Global Energy Transfer Phase changes in the hydrologic cycle play

a role in global transfer of thermal energy The transfer of energy warms the air, which

rises This can cause thunderstorms or hurricanes

Different specific heat capacities (we will get to this in a minute) of the Earth’s different surfaces (sand, water, forests, etc) affect how much they heat up the air and water around them.

How does all this affect weather and climate?

The Earth’s water absorbs a lot of heat from the surroundings when condensing, and it releases a lot of heat when it is evaporating.

How does this affect our weather and climate?

If you think of all the water that is condensing or evaporating all over the lakes, ponds, streams, oceans and clouds that’s a lot of heating and cooling!

Energy Transfer Types Heat of fusion

◦ Energy absorbed when 1 mol of a substance changes from solid to liquid

Heat of Solidification◦ Energy released when 1 mol of a substance

changes from liquid to solid Heat of Vaporization

◦ Energy absorbed when 1 mol of a substance changes from liquid to vapor

Energy Transfer Types cont… Heat of Condensation

◦ Energy released when 1 mol of a substance changes from vapor to liquid

Which ones are endothermic? Exothermic?

Specific Heat Capacity Symbolized as “c” Amount of energy needed to raise temp of 1

g of a substance by 1 degree Celsius Water c= 4.19 J/g degree Celsius

◦ This is high What effect might this have on the climate

of Vancouver compared to Calgary?

SUBSTANCE c (J /g oC)Pure water 4.19

Steam 2.02

Ice 2.00

Sea water 3.89

Moist air 1.15

Dry air 1.00

Specific heat capacity is a constant and is represented

by “c”

Pg. 375

Q = mcΔT

c = specific heat capacity J/goCΔT = change in temperature oCm = mass g Q = amount of heat J

If data are given in initial (T1) and final (T2) temperatures instead of change in temperature, calculate ΔT using ΔT = T2 – T1

Formula

a) The Earth’s land or water surface heats up as it absorbs solar radiation.

b) This thermal energy is transferred by conduction to surrounding cooler air or water causing convection currents in air and

water

THE EFFECTS OF SPECIFIC HEAT CAPACITY ON THE EARTH’S WEATHER

AND CLIMATE

Convection (transfer of thermal energy in fluids – liquids or gases)

Convection currents – air circulates and distributes heat (remember warm air is less dense, rises, cooler air descends and takes its place close to the ground, it heats up…etc.

Practice A 50.0 g mass of water at 25.0 °C is heated

to 50.0°C on a hot plate. Given that the theoretical specific heat capacity of water is 4.19 J/g°C, determine the value for Q

Answer: 5.24 J

Practice How much thermal energy must be released

to decrease the temperature of 1.00 kg of water by 10.0 °C, given that the theoretical specific heat capacity of water is 4.19 J/g°C?

Answer: 41.9 kJ

Practice When 21.6 J of thermal energy is added to a

2.0 g mass of iron, the temperature of the iron increases by 24.0°C. What is the experimental specific heat capacity of iron?

0.45 J/g°C

Why is the ice and water absorbing energy with no change in temperature?

Heat of Fusion, Heat of Vaporization: Phase Changes of

Water

Energy required for melting Energy required for vaporizing

Q = nHfus Q = nHvap

Q amount of heat energy J (joules)

n number of moles (no units)

Hfus heat of fusion J/mol Hvap heat of vaporization J/mol

Calculations

Energy Transfer Graph

Where on the graph would we label heat of fusion? Heat of vaporization?

Calculating Heat of Fusion

Hfus = _Q_

n

Hfus = heat of fusion (kJ/mol)

Q = quantity of thermal energy (kJ)n = amount of the substance (mol)

Practice When 27.05 kJ of thermal energy is added

to 4.50 mol of ice at 0.0°C, the ice melts completely. What is the experimental heat of fusion of water?

Answer: 6.01 kJ/mol

Practice When 5.00 g of ice melts, 1.67 kJ of thermal

energy is absorbed. Calculate the experimental heat of fusion of ice. The molar mass, M, of ice is 18.02 g/mol.

Answer: 6.0 kJ/mol

Practice When 0.751 kJ of thermal energy is added

to 0.125 mol of ice at 0.0°C, the ice changes phase. Calculate the experimental heat of fusion of ice.

Calculating Heat of Vaporization

Hvap = _Q_

n

Hvap = heat of vaporization (kJ/mol)

Q = quantity of thermal energy (kJ/mol)n = amount of the substance (mol)

Practice When 150 g of water changes from liquid to

vapor phase, 339 kJ of energy is absorbed. Determine the experimental heat of vaporization of water, given that the molar mass, M, of water is 18.02 g/mol

Answer: 40.7 kJ/mol

Practice When 8.70 kJ of thermal energy is added to

2.50 mol of liquid methanol, all the methanol enters the vapor phase. Determine the experimental heat of vaporization of methanol.

Specific Heat Practice problems # 1-8 pg. 379

Pg 386/387, try practice problems

Assignment