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**Investigating The Variables of a Gas**

The Chemistry of the Gas Laws

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The Variables of a Gas Gases can be described using four different variables: Temperature Pressure Volume Amount of Gas Explore each of these variable individually by clicking on the buttons below Amount of Gas Temperature Pressure Volume

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Temperature Temperature is a measure of a gas particle’s kinetic energy (energy of motion) Represented by the letter T Temperature can be measured in degrees Celsius (ºC) or Kelvins (K) In chemistry we will measure temperature in Kelvins To convert a Celsius temperature into Kelvins add 273 Ex. 10 ºC = 283 K

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Pressure Gas pressure is caused by the force of gas particles running into the walls of their container Represented by the letter P There are three units of pressure : Kilopascals (kPa), Atmospheres (atm), Millimeters of Mercury (mmHg) We will use kPa as our standard unit Standard pressure is kPa or 1 atm

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Volume The volume of a gas describes the three dimensional space occupied by the particles of a gas Represented by the letter V The volume of a gas is measured in liters (L) Assume that if the volume of a gas changes, the walls of the container are movable. A fixed volume assumes that the container is thick and rigid.

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Amount of Gas The number of particles in a sample of gas affects the pressure and volume of a gas Represented by the letter n The amount of gas is measured in moles (mol)

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**Relationship to pressure**

Remember that gas pressure is caused by the force of gas particles running into the walls of their container and one another As the volume of the container is increased, the pressure in the container decreases because there are less collisions As the temperature of the gas increases, the pressure increases because particles are moving more quickly. This increases the number of collisions As the number of particles in a gas increase, collisions also increase. The causes an increase in pressure

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The Gas Laws The Gas Laws are mathematical equations that were developed in the early 18th century to explain the relationships between the variables of a gas. Click on the buttons below to explore each law. Boyle’s Law Charles’ Law Gay-Lussac’s Law

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Boyle’s Law Boyle’s Law relates the variables of pressure and volume According to this law, as the volume of a container decreases, the pressure of the gas increases This is an inverse relationship The equation for Boyle’s Law is written as: P1V1 = P2V2

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Real World Example A real world example of Boyle’s Law involves squeezing a balloon As the balloon is squeezed the volume of the container decreases This increased the gas pressure inside the balloon If the pressure becomes too great the balloon pops

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Boyle’s Law Demo Watch the following YouTube video to see Boyle’s Law in action

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**Boyle’s Law Calculation**

If we have 4 L of methane gas at a pressure of kPa, what will be the pressure of the gas if we squish it down so it has a volume of 2.5 L? P1 = kPa V1 = 4 L P2 = ??? V2 = 2.5 L P1V1 = P2V2 101.3 x 4 = P2 x 2.5 405.2 = P2 x 2.5 ÷ ÷2.5 kPa = P2 Return to Gas Laws

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Charles’ Law Charles’ Law relates the variables of volume and temperature According to this law, as the temperature of a gas decreases, the volume of the gas also decreases This is a direct relationship The equation for Charles’ Law is written as: V1/T1 = V2/T2

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Real World Example A real world example of Charles’ Law is lower tire pressure in the winter During the winter months, the average outdoor temperature decreases This decrease in temperature causes gas particles to move closer together This decreases the volume of the gas inside the tire

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Charles’ Law Demo Watch the following YouTube video to see Charles’ Law in action

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**Charles’ Law Calculation**

If we have 2 L of methane gas at a temperature of 313 Kelvin, what will the volume be if we heat the gas to 353 K? V1 = 2L T1 = 313 K V2 = ??? T2 = 353 K V1/T1 = V2/T2 2 ÷ 313 = V2 ÷ 353 0.006 = V2 ÷ 353 x x 353 2.25 L= V2 Return to Gas Laws

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**Gay-Lussac’s Law P1/T1 = P2/T2**

Gay-Lussac’s Law relates the variables of pressure and temperature According to this law, as the temperature of a gas decreases, the pressure of the gas also decreases This is a direct relationship The equation for Gay Lussac’s Law is written as: P1/T1 = P2/T2

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Real World Example A real world example of Gay-Lussac’s Law is throwing an aerosol can in a fire When the can hits the fire the temperature of the gas increases This increase in temperature causes an increase in pressure Since the volume of the can is constant, it will eventually explode

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Gay Lussac’s Law Demo Watch the following YouTube video to see Gay Lussac’s Law in action

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**Gay Lussac’s’ Law Calculation**

A gas has a pressure of 93.2 kPa at 313 K. What is the temperature at kPa? P1 = kPa T1 = 313 K P2 = kPa T2 = ??? P1/T1 = P2/T2 93.2 / 313 = / T2 Cross Multiply 93.2 x T2 = x 313 93.2 x T2 = ÷ ÷93.2 T2 = K Return to Gas Laws Quiz

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Quiz Are you ready to take the quiz??? If not, go back and review the gas laws first.

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**Question 1 A. Boyle’s Law B. Charles’s Law C. Gay-Lussac’s Law**

Which Gas Law is illustrated in the problem below? A weather balloon was initially at a pressure of kPa, and its volume was 35.0 L. The pressure is decreased to 76 kPa without loss of gas or change in temperature. What is the new volume? A. Boyle’s Law B. Charles’s Law C. Gay-Lussac’s Law D. None of the Above

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**Go Back and Review the Gas Laws**

Try Again! Go Back and Review the Gas Laws

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CORRECT!!!

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**Question 2 A. 27.6 L B. 27.6 kPa C. 44.3 L D. 44.3 kPa**

A weather balloon was initially at a pressure of kPa, and its volume was 35.0 L. The pressure is decreased to 76 kPa without loss of gas or change in temperature. What is the new volume? A L B kPa C L D kPa

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**Go Back and Review the Gas Laws**

Try Again! Go Back and Review the Gas Laws

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CORRECT!!!

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Question 3 A man heats a balloon in the oven. If the balloon initially has a volume of 0.4 liters and a temperature of 293 K, what will the volume of the balloon be after he heats it to a temperature of 523 K? A L B L C L D L

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**Go Back and Review the Gas Laws**

Try Again! Go Back and Review the Gas Laws

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CORRECT!!!

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**Question 4 Which gas law is illustrated by the following scenario?**

A balloon shrinks when you take it outside on a cold day A. Boyle’s Law B. Charles’ Law C. Gay-Lussac’s Law D. None of the Above

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**Go Back and Review the Gas Laws**

Try Again! Go Back and Review the Gas Laws

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CORRECT!!!

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PTV Sticks Watch the following YouTube video. After viewing the video you should create your own PTV stick using a piece of paper and a marker

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Using your PTV Sticks Now that you’ve created your own PTV stick, go through the following scenarios to see why these relationships are important in the real world. Try to come up with your own explanation using the PTV stick before clicking ahead to the answers

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When a ping pong ball gets dented, the dent can be removed by placing the ball in hot water. If volume is held constant, why does this work?

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If volume of the container is held relatively constant, as the temperature of the gas inside the ball increase, the pressure also increases. This pushes out the dent (Gay- Lussac’s Law)

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As air bubbles rise to the surface of the ocean, their volume increases. Assuming the water temperature is relatively constant as the bubbles rise, why does this occur?

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**As the bubbles rise there is less water above them**

As the bubbles rise there is less water above them. This reduces the pressure on the bubbles allowing them to expand. Therefore the volume increases. (Boyle’s Law)

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Why does a hot air balloon rise when the air inside the balloon is heated. Assume the surrounding air pressure is relatively constant as the balloon rises.

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**As the air is heated, the air molecules expand**

As the air is heated, the air molecules expand. As they expand, the air volume increases and becomes less dense than the cooler surrounding air. This allows the balloon to rise. (Charles’ Law)

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Assuming the volume of the tire is held relatively constant, why would it be best to take your tire pressure before you drive?

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**As you drive the temperature of the air in your tires increases**

As you drive the temperature of the air in your tires increases. As the temperature increases the gas molecules spread out and create a higher tire pressure. (Gay-Lussac’s Law)

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Why does blood enter a syringe when the plunger of the syringe is pulled out? Assume the temperature in the syringe remains constant

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**As the plunger is pulled out the volume of the container increases**

As the plunger is pulled out the volume of the container increases. As the volume increases, the pressure inside the syringe decreases, therefore creating a suction effect and drawing the blood in. (Boyle’s Law)

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Now it’s your turn! Come up with at least two real world scenarios that relate to the gas laws. Once you have come up with your examples get them checked by Mrs. Turner and then add them to the class wiki

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