Ideal Gases Etc

8/6/2019 Ideal Gases Etc

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Resource Guide- Ideal Gases/Acid rain & the

Greenhouse Effect


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Contents

Title Page 1

Contents Page 2

Student learning outcomes Page 3

States of Matter Page 4

Introduction to Ideal Gases Page 58

Convection currents Page 9

Introduction to Acid Rain Page 10 & 11

Introduction to The Greenhouse Effect Page 12 & 13

Experiment 1: Convection Currents Page 14 - 16

Experiment 2: Making Acid Rain Page 17 - 20

Experiment 3: The Albedo Effect Page 21

Glossary Page 22

References Page 22


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Student learning outcomes

- What is a gas?- The ideal gas laws and how to use them.

- What is acid rain?- How is acid rain formed?

- What is the greenhouse effect?- What are the greenhouse gases and what do they do?

- Density based on temperature within a state of matter.


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States of Matter

The three main states of matter are Gases, Liquids and Solids.

Gases, liquids and solids are all made up of tiny particles. These particles act

differently in the three phases. The images below show these different behaviours.

Microscopic view of a

gas.


liquid.


solid.

Particles in a - gas are well separated with no regular arrangement. They vibrate and

move freely at high speeds.Pressure is due to the gas molecules

colliding with the walls of a container.

- liquid are close together with no regular arrangement. They vibrate,

move about, and slide past each other.

- solid are tightly packed, usually in a regular pattern. They vibrate

(jiggle) but generally do not move from place to place.

(Purdue University, 2010)

The following table describes the properties of the 3 above mentioned states of

matter:(Purdue University, 2010)

Some Characteristics of Gases, Liquids and Solids and the Microscopic

Explanation for the Behaviour

Gas Liquid Solid

Takes on the shape and

volume of its container

particles can move past

one another

Takes on the shape of the

part of the container

which it occupies

particles can move/slide

past one another

Maintains a fixed volume

and shape

rigid - particles locked

into place

Compressible

lots of free space between

particles

Not easily compressible

little free space between

particles

Not easily compressible

very little free space

between particles


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Ideal Gases

What is an Ideal gas?For a gas to be considered ideal it must possess both of the following traits:

1. The space the gas molecules occupy is insignificant when compared with the space

in between the gas molecules.(Bellevue College, 2010)

This statement follows that the volume of space that the particles dwell in is

practically nonexistent in comparison to the mass amount of space around andbetween each particle. So although the gas molecules do have a volume, it is so smallcompared to the volume in between gas molecules that it really doesn't matter.

2.Intermolecular forces between gas molecules are negligible. (Bellevue College, 2010)

This statement follows that gas molecules are moving so rapidly that they zip past

each other before having time to be attracted or repelled by one and other. Therefore,

even if certain gas molecules are attractive or repulsive to each other, it doesn't matterbecause they move past each other too quickly to notice it.

When is a gas not ideal?

At exceptionally high pressures, the first above listed trait fails. When gases are

packed under a great deal of pressure, the space between them becomes small. It's

like the difference between having 100 balloons in a large room, and then forcing

them into a much smaller room. Because at this stage their volume cannot be ignoredas it is not so small in comparison to the space around them.

When exposed to extremely low temperatures, gas particles move much slower. In

fact, they move so slow that they no longer zip past each other too quickly to notice

the attractions or repulsions that might exist. So this is when the second above listedtrait fails.


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What is the ideal gas equation?

PV=nRT

This equation has the ability to link all the essential properties of gases together.

P is the pressure (measured in atm) V is the volume (measured in litres) n is the number of moles (measured in moles) R is the ideal gas constant (0.08206) it is not a variable and therefore never

changes T is the temperature in Kelvin (Degrees Celsius + 273). P is pressure (often measured in atmospheres (atm), but can also be measured

in Pascals).

Where does the ideal gas equation come from?

The Ideal gas equation was derived from a combination of several different gas laws.

Boyle's LawBoyles law refers to the relationship between absolute pressure and volume of a gas.

It states the volume of a definite quantity of dry gas is inversely proportional to thepressure, provided the temperature remains constant (Oracle, 2010).

This law can be expressed as P1V1 = P2V2

V1 is the original volume V2 is the new volume P1 is original pressure P2 is the new pressure

Eg. If you have a gas with a volume of 45.0 ml and a pressure of 760mm. If the

pressure is increased to 800mm and the temperature remains constant then according

to Boyle's Law the new volume is 42.75 ml.

- (760mm)(45.0ml) = (800mm)(V2)- V2 = (760mm)(45.0ml) / (800mm)- V2 = 34200 / 800- V2=42.75ml


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Charles's Law

Charless Law refers to the relationship between temperature and volume. He noticedthat as the temperature of a gas increased, the volume increased

This law states that the volume occupied by any sample of gas at a constant pressureis directly proportional to the absolute temperature. (Oracle, 2010)

This law can be expressed as V / T = constant

V is the volume T is the absolute temperature (measured in Kelvin)

Charles's Law can be rearranged into two other useful equations.

V1 / T1 = V2 / T2

V1 is the initial volume T1 is the initial temperature V2 is the final volume T2 is the final temperature

V2 = V1 (T2 / T1)

V2 is the final volume

T2 is the final temperature V1 is the initial volume T1 is the initial temperature (Oracle, 2010)

Avogadro made, perhaps, the most obvious correlation by linking n with V. He

showed that as the number of moles increased, the volume they occupied increased.

Again, this makes perfect sense. The more of anything you have, the more space itwill require. In other words, V= constant x n.

Avogadro's LawAvogadros Law refers to the relationship between n and V or moles and volume,

showing that as the number of moles increased, the volume they occupied also did.The easiest way to quantify the amount of gas is as a mass.


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Calculations using the ideal gas equation

1. Calculations where one variable is missing.

These equations are normally worded along the lines of:

"A gas cylinder of volume ___ contains ___ moles of an ideal gas at ___

temperature. What is the pressure inside the cylinder."

Alternatively, you may be provided with T, P, and n, and ask for V, or any

combination thereof.

For this type of question as you have three of the four variables, you simply need to

solve for the fourth. It's just a case of plugging your given values into the equation.

Start by writing "PV=nRT" and then fill in the values you have been given or already

know (such as that R will always be 0.08206) and then solve for the one that's still

missing. It is important to keep track of units as you do this, as it is easy to make a

mistake here.

2. Calculations where two variables are changed.

In this case, there is a "before and after" situation. Two of the variables are kept the

same, and two are changed. The simplest way to go about solving such an equation is

to group the things that change on one side of the equation, and the things that don'tchange on the other side.

Example: A box containing a sample of gas at 1.00 atm is heated from 270K to

300K. What happens to the pressure inside the box?

Answer: the volume of the box (V) and the number of moles inside the box have not

changed. The temperature and the pressure have changed. So re-write PV=nRT

rearranged such that these two sets are grouped on either side . . . P/T = nR/V. Now,since the entire expression nR/V does not change, P/T for the "before" situation must

equal P/T for the "after" situation. (AUS-e-TUTE, 2011)

Another way to write this equation mathematically is P1 x T1 = P2 x T2

Then when we plug in our given values, we have the equation

- (1.00 atm)/(270K) = (P2)/(300K)- P2 = [(1.00 atm)/(270K)] x 300K- P2 = 1.11atm

To double check your answer you should always consider does your answer make

sense given the situation? So since the temperature has been raised, as a result thepressure should go up. This is the case as we are following one of the abovementioned gas laws where, a rise in temperature must correspond with a rise inpressure.


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Convection currents

Convection currents are a cyclic process of the flow of heat through a movement of

matter from a hot region to a cool region.

For example, if we were to heat up a region of air, as this air heats, the molecules

spread out, causing this region to become less dense than the surrounding, unheated

air. When air is less dense it is also less heavy and therefore rises. As it rises, it

reaches cooler regions and thus begins to cool itself. Eventually with the cooling of

the air, it starts to become more dense and therefore heavier and so it will begin to

fall. But in the mean time other air molecules have been heated and have began to

rise taking the original rising molecules place in a continuous cycle where they will

then eventually cool and fall as well.


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Acid rain

"Acid rain" is a broad term referring to a mixture of wet and dry deposition

(deposited material) from the atmosphere containing higher than normal amounts of

nitric and sulfuric acids. (EPA, 2007)

The formation of acid rain is a result of both natural causes and manmade, but

ultimately is when rain is made acidic by pollutants in the air. Some natural sources

include volcanoes and decaying vegetation. The manmade sources, are mainly

emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx). through the burning of

fossil fuels (such as coal to produce electricity) or the exhaust from vehicles.Acid rain occurs when these gases react in the atmosphere with water, oxygen, and

various other chemicals to form different acidic compounds.

Sulphur and nitrogen oxides produced when oil, coal, natural gas or peat were

burned could be converted in the atmosphere into sulphates and nitrates, and then into

acids, which could return to earth in contaminated rain, snow, hail, fog or mist.

McCormick, J, (1954. Pg 1)

Wet Deposition

Wet deposition refers to acidic fog, snow, and rain. If the acid compounds in the air

are blown into areas where the weather is wet, they can fall to the ground in the formof rain, snow, fog, or mist. As this acidic water flows over and through the ground, itaffects a variety of plants and animals.


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Dry Deposition

In areas where the weather is dry, the acid chemicals may become incorporated intodust or smoke and fall to the ground through dry deposition, sticking to the ground,

buildings, homes, cars, and trees. Approximately 50% of the acidity in the

atmosphere returns back to the earth through dry deposition.

What is acidity?Acidic and basic are two ways that we describe chemical compounds. Acidity is

measured using a pH scale. A pH scale runs from zero (the most acidic) to 14 (the

most basic or alkaline). A substance that is neither basic or acidic is called "neutral",and this has a pH of 7. (EPA, 2007)


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The Greenhouse Effect

The term 'greenhouse gases' is used to refer to the gases in the atmosphere that havethe ability to absorb the radiations released off the earths surface from the sun. The

most prominent greenhouse gases in the Earth's atmosphere are water vapour, carbon

dioxide, methane, nitrous oxide, ozone and CFCs.

Greenhouse Effect

The greenhouse effect warms the Earth naturally. To warm the Earth, it relies on the

Sun's energy. When the Sun's energy reaches the Earth's surface, around 49% of it is

absorbed and the rest is reflected back to space. This absorbed energy warms the

Earth's surface, which in turn radiates heat energy back towards the space. While this

warm energy is travelling towards space, it is partially trapped by greenhouse gases.

The trapped energy is then released in all directions, warming the earth's surface and

atmosphere. This process of warming the Earth is known as the greenhouse effect.

Without the greenhouse effect the earth would be around 33 degrees Celsius cooler

than usual. (Buzzle, 2011)

But the greenhouse effect isnt all good. Although it heats up the surface of the

Earth, it simultaneously cools the stratosphere, which eventually triggers ozone layer

depletion. The Ozone layer is very important to human life, considering the vital role

it plays by protecting the earth from UV rays entering the atmosphere.


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Besides the above-stated factors that affect the greenhouse effect, the sunlight's first

encounter with the type of Earth surface, also impacts the greenhouse effect. The

percentage of the heat reflected and radiated back by different Earth surfaces like the

grasslands, forests, glaciers, deserts, cities including the industrial areas, and clouds is

defined as albedo, by atmospheric scientists. The levels of heat radiation range

depends upon the type of Earth's surface, it has reflected back from into the

atmosphere. Cloud cover also plays a vital role by reducing both; the amount of solar

radiation reaching the Earth's surface and the amount of radiation energy emitted

back into the space. (Buzzle, 2011)

Greenhouse Gases

Water Vapour: Water vapour is the gaseous form of water and is produced due to

watersevaporation. It makes up about 33 to 66 percent of greenhouse gases and is

therefore the most prominent constituents of the greenhouse gases list.

Carbon Dioxide: Carbon dioxide is a chemical compound with the chemical formula

CO2. Carbon dioxide is produced in several processes such as, respiration in plants,

animals and humans and combustion of fossil fuels. This gas makes up 9 to 26percent of greenhouse gases.

Methane: Another prominent greenhouse gas is methane. Its molecular formula is

CH4. The ability methane possesses to trap heat is 20 times more than that of carbon

dioxide. It's assumed that the Earth's crust contains huge deposits of methane gas, a

part of which is let out in the process of mining, thus adding to the greenhouse effect.

Methane makes up 4 to 9 percent of greenhouse gases.

Nitrous Oxide: Nitrous oxide is another important greenhouse gas, which can cause a

high impact on global temperatures. The chemical formula of nitrous oxideis N2O.

This gas is an important, naturally occurring regulator of the stratospheric ozone,

which tends to react with the ozone and contribute to greenhouse effect.

Ozone: Another main greenhouse gas is ozone, making up approximately 3 to 7

percent. Ozone, in upper troposphere acts as a greenhouse gas, while at ground level

it acts as an air pollutant. As a greenhouse gas, ozone absorbs the infra red energythat is emitted by the earth.


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Experiment 1 : Convection Currents

Aim: To show that warm air is less dense and therefore less heavy than cold air

Materials:

1 x Small aquarium

4 x Polystyrene cups

4 x Bulldog clips

1 x Needle

Ice water

Tap waterWarm water

Boiling water

Green dye

Blue dye

Yellow dye

Red dye

Method:

Step 1: Half fill the small aquarium with tap water.

Step 2: Using the bulldog clips, attach each of the 4 cups to one of the corners of

the aquarium each. (Make sure the cups are not sitting in the water, but

are just above its surface)


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Step 3: Fill the first cup with ice water and mix in the green dye

Step 4: Add some tap water to the next cup and mix in the blue dye

Step 5: To the third cup add some warm water and mix in the yellow dye

Step 6: For the fourth cup add some boiling water and mix in the red dye

Step 7: Take the needle and poke a small hole into the bottom of each cup so

that the colour solutions can leak into the aquarium

Step 8: Observe the colour distribution. There should be a layering effect

occurring, with the hottest solution on top and the coldest solution on the

bottom

Worksheet:

1. Explain how you think a convection current would work in theatmosphere.

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

2. Draw the layering effect that should have occurred in the experiment.


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Worksheet Answers:

1. Explain how you think a convection current would work in theatmosphere.

As hot air rises due to its lower density, it starts to cool as the temperature

drops at higher altitude and so it therefore becomes denser and starts to

want to fall. In the meantime other hot air would be rising and continuing

the cycle.

2. Draw the layering effect that should have occurred in the experiment.


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Experiment 2 : Making Acid Rain

Aim: To show how acid rain is formed and the effect it has on the environment.

Materials:

Red cabbage

Clear plastic bag

30ml Ethanol

Filter paper

Water tank

2 x Tripod

2 x Gauze mat

Shavings of PVC piping

Top of a tin can

Piece of tin

Piece of wood

Flask

100ml of water

Piping to direct water vapour

Plastic ice tray

Ice

Bunsen burner

Matches

Method:

Step 1: Tear several leaves of red cabbage into small pieces and place them in a clear

plastic bag. Pour in 30ml of ethanol and knead the bag for about 1 minute. (The

leaves will lose their purple colour)

Step 2: Grab some filter paper and add it to the cabbage extract. Once it has taken on

the colour remove it and allow it to dry for 5 minutes. Repeat the process until the

paper is saturated with the colour.


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Step 3: Prepare the materials in the following set up:

Step 4: Place some ice in the ice tray, place the filter paper on the inside tripod andgauze mat and add 100ml of water to the flask outside the tank and begin to boil it.

Step 5: with everything in position, use a match to ignite the PVC shavings (acid rain

source)

Step 6: Once the PVC has completely burnt, gently tap the plastic tray. The droplets

that have formed through condensation should fall and hit the filter paper.

Step 7: Take note of any colour changes.


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Worksheet:

1. Why do you think the filter paper changed colour as the water dropletslanded on it?

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

2. What do you think would happen if the same experiment was donewithout burning the PVC shavings?

_________________________________________________________

_________________________________________________________

_________________________________________________________

________________________________________________________

3. What do you thing the filter paper is representing in this experiment forin the natural environment?

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________


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Worksheet Answers:

1. Why do you think the filter paper changed colour as the water dropletslanded on it?

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

2. What do you think would happen if the same experiment was donewithout burning the PVC shavings?

It would just be a small scale model making normal rain!What do you think the filter paper is representing in this experiment for in

the natural environment?

The plants that are effected by acid rain, and lose their pigmentation due to

the chemical reaction.


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Experiment 3 : The Albedo Effect

Aim: To show that the surface the incident radiation hits on the earth affects the

reflected radiation.

Materials:

2 x Aluminium pans (approx. 15 x 25 x 3cm) one painted black and the other white

1 x Small torch

1 x Retort stand

1 x Clamp

1 x 50cm piece of string1 x Protractor

1 x Lux metre

Method:

Step 1: Starting off with the white pan, set up the retort stand to hold the torch

so that it is focussing on the centre of the pan.

Please note: The light must be at a 30 degree angle from the location of

the clamp, and the distance from where the light shines from the torch to

the pan must be 50cm.

Step 2: Using a Lux metre measure the incident radiation and record the value.

The position you choose to measure this vale must be used throughout

out all recordings in this experiment.

Step 3: Move the Lux metre so that you can record the reflected radiation (Dont

forget to flip the Lux metre over for this recording)

Step 4: Repeat steps 2 and 3 for a few different surfaces, first the black pan, then

the black pan filled with 2 centimetres of water and finally with crushed

ice. Make sure you record all readings to determine and compare the

Albedo.


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Glossary

Atmosphere: The air or gases that surround the Earth

Base: Any of a large group of chemicals with a pH greater than 7. Examples are

ammonia and baking soda.

Emissions: The gases that are released when fossil fuels are burned.

Neutral: A substance that is neither an acid nor a base and has a pH of 7. Neutral

substances can be created by combining acids and bases.

References

- AUS-e-TUTE, 2011, Chemistry Tutorial : Ideal Gas Law, viewed 5th June2011

- Bellevue College, 2010, Science DivisionIdeal Gases, viewed 7th June 2011http://scidiv.bellevuecollege.edu/bg/ideal.html

- Buzzle, 2011, Greenhouse Gases, viewed 4 th June 2011,http://www.buzzle.com/articles/greenhouse-gases-list.html

- McCormick, J.1954,Acid EarthThe global threat of acid pollution, 2nd edn,Earth Publications Limited, London

- Oracle - Think quest, 2010, ChemWeb, viewed 7th June 2011

- Purdue University, 2010, States of Matter, viewed 5th June 2011

- Taylor, F.W 2005,Elementary Climate Physics, 1st edn, Oxford UniversityPress Inc., New York.

- EPA, 2007,Acid Rain, viewed 4th June 2011http://www.epa.gov

By Katherine Strangos
http://scidiv.bellevuecollege.edu/bg/ideal.htmlhttp://scidiv.bellevuecollege.edu/bg/ideal.htmlhttp://www.buzzle.com/articles/greenhouse-gases-list.htmlhttp://www.buzzle.com/articles/greenhouse-gases-list.htmlhttp://www.epa.gov/http://www.epa.gov/http://www.epa.gov/http://www.epa.gov/http://www.buzzle.com/articles/greenhouse-gases-list.htmlhttp://scidiv.bellevuecollege.edu/bg/ideal.html

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