Science 10 Daily NotesScience 10 Daily Notes

Section 13.2 pgs 427-434Section 13.2 pgs 427-434

Energy and WaterEnergy and Water

Most of sun’s energy hits the oceansMost of sun’s energy hits the oceansAmount of reflected solar radiationAmount of reflected solar radiation Snow: 90%Snow: 90% Ice: 50%Ice: 50% Liquid water (lakes, rivers, oceans): 7%Liquid water (lakes, rivers, oceans): 7%

Why do bodies of liquid water not change Why do bodies of liquid water not change temperature, even though they absorb temperature, even though they absorb 93% solar radiation?93% solar radiation? Due to unique properties of waterDue to unique properties of water

Water has many unique characteristics.

One of these properties is water’s unusual ability to absorb large quantities of heat without much change in temperature.

This characteristic is the specific heat capacity. .

Unique Properties of WaterUnique Properties of Water

1.1. Specific heat capacity – next slideSpecific heat capacity – next slide

2.2. Heat of vaporization – amount of energy Heat of vaporization – amount of energy required to convert water from a liquid to required to convert water from a liquid to a gas (evaporation)a gas (evaporation)

3.3. Heat of fusion – amount of energy Heat of fusion – amount of energy required to convert a solid to a liquid required to convert a solid to a liquid (melting)(melting)

Specific Heat CapacitySpecific Heat Capacity

Amount of heat required to raise the temp of 1g Amount of heat required to raise the temp of 1g of a substance by 1 degree Cof a substance by 1 degree C Formula: Q = mcFormula: Q = mc∆t∆t

Q = amt of heatQ = amt of heat

M = mass of substanceM = mass of substance

C = specific heat capacity C = specific heat capacity

∆∆t = temp changet = temp change If a substance has a high specific heat capacity, then If a substance has a high specific heat capacity, then

the substance will need a lot of energy to change its the substance will need a lot of energy to change its temperaturetemperature

Water has a high specific heat capacityWater has a high specific heat capacity

What does it mean to have a high What does it mean to have a high specific heat capacity?specific heat capacity?

It means water has the It means water has the capacitycapacity to hold a to hold a lot of heat without changing temperature lot of heat without changing temperature

The temperature of water increases much The temperature of water increases much less than the temperature of most similar less than the temperature of most similar substances after gaining the same amount substances after gaining the same amount of energy of energy

Large specific = small temperature

heat capacity increase

When water absorbs When water absorbs 4.184 Joules4.184 Joules of heat, the of heat, the temperature of temperature of one gram of waterone gram of water will increase will increase by by 11 C°. C°.

Relatively speaking, this is an enormous amount Relatively speaking, this is an enormous amount of heat energy. of heat energy. Coastal areas like Nova Scotia, which are Coastal areas like Nova Scotia, which are surrounded by water, maintain relatively stable surrounded by water, maintain relatively stable climates with moderate temperatures. climates with moderate temperatures. This is because water can absorb or release a This is because water can absorb or release a great deal of heat without experiencing huge great deal of heat without experiencing huge fluctuations in temperature. fluctuations in temperature. 

By comparison, look at the heat capacity of copper.

1 gram of copper will rise in temperature by 1 C° when just 0.385 Joules of heat is absorbed.

This low specific heat capacity indicates that copper is a good conductor of heat. You might predict that applying a small amount of heat will make the temperature of a gram of copper skyrocket while the same amount of heat hardly makes the temperature of one gram of water rise at all.

Q = mcQ = mcΔΔTT

Use this to find out the mass, energy, or Use this to find out the mass, energy, or temperature change of a specific temperature change of a specific substance as it gains or loses energy.substance as it gains or loses energy.

Chemistry: Specific Heat CapacityChemistry: Specific Heat Capacity

Q = mQ = mΔΔHH00vapvap

Use this to find the mass or energy of a Use this to find the mass or energy of a specific substance as it changes state specific substance as it changes state from liquid to gas (vaporization)from liquid to gas (vaporization)

When vaporization occurs, the When vaporization occurs, the temperature will remain the same.temperature will remain the same.

A negative energy would occur for A negative energy would occur for condensation (gas to liquid)condensation (gas to liquid)

Q = mQ = mΔΔHH00fusfus

Use this to determine the mass or energy Use this to determine the mass or energy when a substance changes from solid to when a substance changes from solid to liquid (fusion = melting)liquid (fusion = melting)

There is no temperature change while the There is no temperature change while the substance is melting substance is melting

A negative Q (energy) would be recorded A negative Q (energy) would be recorded if the substance solidified (liquid to solid)if the substance solidified (liquid to solid)

Water in the AirWater in the AirSaturated = full to capacitySaturated = full to capacity

Unsaturated = not full to capacityUnsaturated = not full to capacity

When there is When there is as much wateras much water vapour in the vapour in the air air as possibleas possible at a given temperature, we at a given temperature, we say that the air is saturated.say that the air is saturated.

**Warm air can hold more water vapour than cool air

Formation of Haze, Fog, and Clouds: Condensation Nuclei

The process of condensation of vapor -> water to form a cloud drop is not that simple in the atmosphereNEED Condensation Nuclei to form cloud dropsCondensation Nuclei:

small particles in air created from/by:

dust volcanoes factory smoke forest fires ocean salt sulfate particles from phytoplankton in ocean

They are most abundant in lower troposphere over urban areas

They are quite small relative to a rain drop or cloud drop

QUESTION FOR THOUGHT:QUESTION FOR THOUGHT:

Why does the relative humidity seldom Why does the relative humidity seldom reach 100% in polluted air?reach 100% in polluted air?

Formation of HazeFormation of Haze

Two types:Two types: dry hazedry haze - large/giant particles in the air - large/giant particles in the air

(smoke, smog, dust)(smoke, smog, dust) wet hazewet haze - H2O condenses onto hydroscopic - H2O condenses onto hydroscopic

CCN - can occur at RH's as low as 75%CCN - can occur at RH's as low as 75% wet haze has a dull gray, white colorwet haze has a dull gray, white color

Formation of Fog, IntroductionFormation of Fog, Introduction

Forms as the RH increases to 100% - Forms as the RH increases to 100% - haze particles grow into fog (cloud) haze particles grow into fog (cloud) particles near the groundparticles near the ground

is really a cloud near the groundis really a cloud near the ground

International definitionInternational definition: Visibility is less : Visibility is less than 1 kmthan 1 km

Fog in polluted areas can be a health Fog in polluted areas can be a health problem since it becomes acidicproblem since it becomes acidic

Formation of Radiation Fog - Formation of Radiation Fog - Radiational CoolingRadiational Cooling

Need: shallow, moist air near surface clear/calm nights although light winds will bring more air in contact with

ground Radiational cooling allows the temperature to drop to the dew point

Once the temperature reaches the dew point, radiation Once the temperature reaches the dew point, radiation fog begins to developfog begins to developCommon in the fall - especially when our weather is Common in the fall - especially when our weather is dominated by high pressuredominated by high pressure

often forms in valleys first since this is where the coldest air is often forms in valleys first since this is where the coldest air is - - called called valley fogvalley fog

Humidity

ABSOLUTE HUMIDITY A type of humidity that considers the mass of

water vapor present per unit volume of space. Also considered as the density of the water vapor. It is usually expressed in grams per cubic meter.

RELATIVE HUMIDITY Describes the amount of water vapor that exists

in a gaseous mixture of air and water expressed as a percentage of the maximum amount of water vapor that could be present if the vapor were at its saturation conditions.

Relative HumidityRelative Humidity

The most common way that the amount of water in the The most common way that the amount of water in the air is reported is relative humidity.air is reported is relative humidity.RH is a comparison between the amount of water in the RH is a comparison between the amount of water in the air with the amount of water that could be in the air when air with the amount of water that could be in the air when evaporation and condensation are equal. Mathematically evaporation and condensation are equal. Mathematically RH is a percentage of "the maximum amount of water RH is a percentage of "the maximum amount of water possible at that temp.possible at that temp.For example: 75% r.h. means if air in a room could have For example: 75% r.h. means if air in a room could have 20 liters of water in it, it really only has ________ liters.20 liters of water in it, it really only has ________ liters.If temp increases without adding any water, rh If temp increases without adding any water, rh decreases. If temp decreases, rh increases. Why? The decreases. If temp decreases, rh increases. Why? The amount of water that COULD be in the air changes, so amount of water that COULD be in the air changes, so with the same amount of water, percent changes.with the same amount of water, percent changes.

Calculating the RH requires the correct equation(s). Calculating the RH requires the correct equation(s). The RH is the amount of moisture in the air (via The RH is the amount of moisture in the air (via moisture mass or vapor pressure) divided by the moisture mass or vapor pressure) divided by the maximum amount of moisture that could exist in the maximum amount of moisture that could exist in the air at a specific temperature (via max moisture mass air at a specific temperature (via max moisture mass or saturation vapor pressure). or saturation vapor pressure). RH is expressed as a percentage and has no units RH is expressed as a percentage and has no units since the units in both the numerator and since the units in both the numerator and denominator are the same. The percentage is found denominator are the same. The percentage is found by multiplying the ratio by 100%. The RH is NOT the by multiplying the ratio by 100%. The RH is NOT the dewpoint divided by the temperature. dewpoint divided by the temperature. For example, if the temperature was 60 F and the For example, if the temperature was 60 F and the dewpoint was 30 F, you would not simply take dewpoint was 30 F, you would not simply take (30/60)*100% = 50% RH.(30/60)*100% = 50% RH.

Dewpoint and Relative HumidityDewpoint and Relative Humidity

Dewpoint is the temperature at which Dewpoint is the temperature at which condensation occurs. The more water condensation occurs. The more water vapor that is in in air, the higher this vapor that is in in air, the higher this dewpoint temperature will be. In other dewpoint temperature will be. In other words, high humidity will result in a higher words, high humidity will result in a higher dewpoint temperature. The dewpoint dewpoint temperature. The dewpoint temperature of air is important in weather temperature of air is important in weather forecasting because it indicates how high forecasting because it indicates how high air must rise in order for clouds to begin air must rise in order for clouds to begin condensing from that air.condensing from that air.

Use your water vapor (dewpoints) graph: Use your water vapor (dewpoints) graph: 1. How much water (at most) could be in the air at 20 1. How much water (at most) could be in the air at 20 degrees: _________ . If it really only has 7 g/kg, then the degrees: _________ . If it really only has 7 g/kg, then the rh is: __________ .rh is: __________ .  2. This air has a dewpoint of ________ .2. This air has a dewpoint of ________ .  3. If the air in the previous example rose into the 3. If the air in the previous example rose into the atmosphere and cooled at the rate of 7 degrees Celcius atmosphere and cooled at the rate of 7 degrees Celcius per kilometer of altitude, at what altitude would per kilometer of altitude, at what altitude would condensation and cloud formation occur?condensation and cloud formation occur?  

Dewpoint GraphDewpoint Graph

http://www.omega.com/temperature/Z/pdf/http://www.omega.com/temperature/Z/pdf/z102.pdfz102.pdf

What is “Dew Point”?What is “Dew Point”?The warmer air is, the more water vapor it The warmer air is, the more water vapor it can "hold." can "hold."

Dew point is a measure of how much Dew point is a measure of how much water vapor is actually in the air. water vapor is actually in the air.

Relative humidity is a measure of the Relative humidity is a measure of the amount of water in the air compared with amount of water in the air compared with the amount of water the air can hold at the the amount of water the air can hold at the temperature it happens to be when you temperature it happens to be when you measure it. measure it.

Now, let's see how dew point and relative humidity work. Now, let's see how dew point and relative humidity work. Imagine, that at 3 p.m. you measure the air's Imagine, that at 3 p.m. you measure the air's temperature at 30 degrees and you measure its humidity temperature at 30 degrees and you measure its humidity at 9 grams per cubic meter of air. at 9 grams per cubic meter of air. What would happen if this air cooled to 10 degrees with What would happen if this air cooled to 10 degrees with no water vapor being added or taken away? no water vapor being added or taken away? As it cools to 10 degrees the air becomes saturated; that As it cools to 10 degrees the air becomes saturated; that is, it can't hold any more water vapor than 9 grams per is, it can't hold any more water vapor than 9 grams per cubic meter. cubic meter. Cool the air even a tiny bit more and its water vapor will Cool the air even a tiny bit more and its water vapor will begin condensing to form clouds, fog or dew - depending begin condensing to form clouds, fog or dew - depending on whether the air is high above the ground, just above on whether the air is high above the ground, just above the ground, or right at the ground. the ground, or right at the ground. Back at 3 p.m., when we made the measurements, we Back at 3 p.m., when we made the measurements, we could say that the air's dew point is 10 degrees C. That could say that the air's dew point is 10 degrees C. That is, if this particular air were cooled to 10 degrees at is, if this particular air were cooled to 10 degrees at ground level, its humidity would begin condensing to ground level, its humidity would begin condensing to form dew. form dew.

How about relative humidity? How about relative humidity? At 3 p.m. the air has 9 grams of water vapor per At 3 p.m. the air has 9 grams of water vapor per cubic meter of air. We divide 9 by 30 and cubic meter of air. We divide 9 by 30 and multiply by 100 to get a relative humidity of 30% multiply by 100 to get a relative humidity of 30% In other words, the air actually has 30% of the In other words, the air actually has 30% of the water vapor it could hold at its current water vapor it could hold at its current temperature. temperature. Cool the air to 20 degrees. Now we divide 9, the Cool the air to 20 degrees. Now we divide 9, the vapor actually in the air, by 17, the vapor it could vapor actually in the air, by 17, the vapor it could hold at its new temperature, and multiply by 100 hold at its new temperature, and multiply by 100 to get a relative humidity of 53% (rounded off). to get a relative humidity of 53% (rounded off). Finally, when the air cools to 10 degrees, we Finally, when the air cools to 10 degrees, we divide 9 by 9 and multiply by 100 to get a relative divide 9 by 9 and multiply by 100 to get a relative humidity of 100% - the air now has all the vapor humidity of 100% - the air now has all the vapor it can hold at its new temperatureit can hold at its new temperature

Water CycleWater Cycle

Evaporation and condensation are Evaporation and condensation are continually taking placecontinually taking place Source of evaporation (water vapor in air): Source of evaporation (water vapor in air):

Oceans, rivers, lakes, moist ground, living plantsOceans, rivers, lakes, moist ground, living plants Source of condensation:Source of condensation:

Air moves to cooler regions or the air temp lowersAir moves to cooler regions or the air temp lowersWater condenses to form clouds or ice crystalsWater condenses to form clouds or ice crystals

Condensed water eventually falls down to Condensed water eventually falls down to earth as precipitation and returns the water to earth as precipitation and returns the water to the lakes, oceans, etc to be evaporated againthe lakes, oceans, etc to be evaporated again

Answers to homework #1-4 pg 434Answers to homework #1-4 pg 434

1.1. How specific heat capacity influences the How specific heat capacity influences the temp of a large lake.temp of a large lake.

A: It has a high specific heat capacity which A: It has a high specific heat capacity which means that it takes more solar energy to means that it takes more solar energy to change the temperature than air or land. change the temperature than air or land. Also, water mixes and flows freely which Also, water mixes and flows freely which helps maintain a constant temp.helps maintain a constant temp.

Homework…Homework…

2.2. Heat of vaporization: amount of energy Heat of vaporization: amount of energy required to covert 1g of a substance from required to covert 1g of a substance from a liquid to a gasa liquid to a gas

3.3. Converting from a liquid to a solid (water Converting from a liquid to a solid (water freezing) is called heat of fusion.freezing) is called heat of fusion.

4.4. When saturated air cools water will When saturated air cools water will condense out of the air and form clouds.condense out of the air and form clouds.