BASIC QUANTITIES OF GASES

Transcription

1 BASIC QUANTITIES OF GASES PRESSURE (P): Definition: 1 atm = Pa = 1,01325 bar (1 bar = 10 5 Pa) 1 atm = cmhg = mmhg (Torr) Manometer: Barometer: VOLUME (V): Unit: 1

2 NUMBER OF MOLES (n): Avogadro s Number 6, MOLE 1 mole = particles Ex: Convert the following data. a) 0,5 mole = particles b) 3, = mole c) 12, = mole d) 0,01 mole of gas = particles e) 2, = mole /Amedeo_Avogadro TEMPERATURE ( ): Temperature ( ) Absolute Temperature ( ) Unit: Conversion è Application Make all conversions for the following quantities and state each unit that it is belonging to which quantity: a) 0,5 atm = cmhg b) 0,2 L = ml c) 0 C = K d) 12, molecules = mole molecules e) 570 mmhg = atm 2

3 f) 100 cm 3 = L g) 298 K = C h) 30 cmhg = mmhg i) 0,5 moles gas = gas j) 2,5 atm = cmhg k) 3, atoms = moles atoms HOMEWORK: UNIT CONVERSIONS FOR THE GAS LAWS Directions: Complete the following tables, showing your work for each lettered box beside the corresponding letter below. Include units on your work and write your final answers in the tables. TEMPERATURE PRESSURE K o C mm Hg Pa atm 373 K (D) 890 mm Hg (K) (O) (A) 56 o C (G) Pa (P) (B) 154 o C (H) (L) 0.64 atm 128 K (E) 3140 mm Hg (M) (Q) 800 K (F) (I) (N) 2.35 atm (C) 10 o C (J) Pa (R) (A) (J) (B) (K) 3

4 (C) (L) (D) (M) (E) (N) (F) (O) (G) (P) (H) (Q) (I) (R) 4

5 GAS LAWS BOYLE S LAW: Exp- The Distortion of Marshmallows: Draw a face on a marshmallow. Remove the plunger and put the marshmallow inside the syringe. With the end open, replace the plunger and slowly push it so it barely touches the marshmallow. Cover the opening with your finger and slowly pull the plunger. Let the plunger move back down. Explain what you think is happening on your sheet. Draw how the air particles look in the marshmallow before and after the change. Application: Use link or use the QR code to go to the web site: Other simulation page: Use the simulation to construct the knowledge about V and T relationship. - Look at the gas in the container and change its volume by dragging the V part. - Record the pressure and temperature of gas. - Repeat to change the volume at least 3 more times and record all data: Trial Volume (L) Pressure (atm) - Draw a graph for P versus V: P - Write the relation between P and V: - Write the mathematical equation for the relation between P and V: Question: The pressure of some amount of O 2 gas in the 4 L container is 3 atm. So what would be the new pressure of this O 2 gas if the volume of its container is made 2 L at the same temperature? (Write the given data first) V 5

6 CHARLES LAW Exp- The Balloon in the Bottle: Find an empty glass bottle, such as a soda bottle, and fill it with about an ounce of water. In a pan of water, heat the bottle until the water inside reaches a boil. Stretch balloon over the mouth of the bottle. As the bottle cools, the gas will suck the balloon into the bottle and it will begin to inflate inside the bottle. What is happening is that the balloon trapped the water vapor in the bottle and as it cools the outside air pressure replaces the water vapor that is now condensing and emptying the inside of the bottle. Gas expands as it heats, and shrinks as it cools, making the bottle empty compared to the exterior air pressure. The balloon expands inside the bottle to allow the exterior air pressure inward. What did you observe? Draw how the air particles look in balloon before and after the change. Application: Use the simulation to construct the knowledge about P and V relationship. - Look at the gas in the container and change its temperature by dragging T button. - Record the new volume of gas. - Repeat to change the temperature at least 4 times. Record the data. Trial Temperature ( K) Volume (L) temperature ( C) - Draw a graph for V versus T Draw a graph for V versus t V V T ( ) t ( ) - Write the relation between V and T: - Write the mathematical equation for the relation between V and T: 6

7 Question: The volume of N 2 gas in an isobaric container is 6 L at 27 C. So, what would be the last volume of this N 2 gas when its temperature is increased to 127 C? (Write the given data first) GAY-LUSSAC S LAW: Use the simulation to construct the knowledge about P and T relationship. - Look at the gas in the container and change its temperature by dragging T button. - Record new pressure of gas. - Repeat to change the temperature at least 4 times. Record all data: Trial Temperature (K) Pressure (atm) - Draw P T and also P t graphs: P P T ( ) t ( ) - Write the relation between P and T: - Write the mathematical equation for the relation between P and T: Question: The pressure of a gas in the glass container is 2 atm at -23 C. So, what will be the last pressure of the same gas when its temperature is increased to 77 C? (Write the given data first) 7

8 AVOGADRO S LAW: This law is related with the mole number of gas and its Pressure or its Volume as: If n is increased so the pressure of the gas is (T and V constant) So the mathematical equation is: If n is increased so the volume of the gas is (T and P constant) So the mathematical equation is: Reflection Gas Laws Worksheet from The Answer Key of the worksheet: ml K 2-2,22 L 8-30 L L 9-31 L 4-26,6 L 10- a) 0,14 atm b) 4,5 atm mmhg 11- a) 39,4 L b) 14,9 L 6-0,0313 atm 12- a) 0,0646 moles b) 0,030 moles 8

9 HOMEWORK: Behavior of Gases Solve the following problems. Show your work and include correct units for full credit. 1. A gas has an initial volume of 15 L. If the temperature increases from 330 K to 450 K, find the new volume. 2. A gas exerts 1.2 atm of pressure. If the temperature is raised from 25 C to 100 C, find the new pressure. 3. A sample of oxygen takes up 34 dm 3 of space when it is under 500 kpa of pressure. When the pressure is changed to 340 kpa, find the new volume. 4. The pressure of some N 2 drops from 315 kpa to 220 kpa. If the initial volume is 1.4 L, find the new volume. 9

10 5. The pressure of neon changes from 786 mm Hg to 1811 mm Hg. If the initial temperature 87 C, what is the new temperature (in C)? 6. When the temperature of a gas changes, its volume decreases from 12 cm 3 to 7 cm 3. If the final temperature is measured to be 18 C, what was the initial temperature (in C)? Answers: L atm dm L C C 10

11 HOMEWORK: PROPERTIES OF GASES 1. Gases can be defined by the following statement: A. Gases freely flow to fill the container they are in. B. Gases have neither a defined volume nor shape. C. Gases are highly compressible. D. All of the above 2. The relationships between the following four variables are known as the gas laws. A. pressure (P), depth (D, in cm), temperature (T), and amount (n, in moles) B. pressure (P), volume (V), temperature (T), and amount (n, in moles) C. height (H, in cm), volume (V), temperature (T), and amount (n, in moles) D. pressure (P), volume (V), length (L, in cm), and amount (n, in moles) 3. Gas molecules are incredibly far apart and often interact with each other. False True 4. The scientific principle that, so long as temperature is kept constant, the volume (V) of a fixed amount of gas is inversely proportional to its pressure (P) is called: A. Boyles's Law B. Charles's Law C. Avogadro's Law D. Ideal Gas Equation 5. The scientific principle that states that when pressure is kept constant, a fixed amount of gas increases its volume as its temperature increases is known as: A. Boyle s Law B. Charles's Law C. Avogadro's Law D. Ideal Gas Equation 6. In 1811, Avogadro put forth a hypothesis stating that A. Atoms combine in whole-number ratios to form molecules. B. Gases increase their volume in the same amount when their temperature is increased by the same degree. C. Equal volumes of different gases have different numbers of molecules. D. Equal volumes of different gases have an equal number of molecules. 7. Suppose you have two identical birthday balloons, with one filled with the gas helium and the other blown up by you. Assuming they re both filled to the same amount, these balloons will have the same number of molecules. True False 8. When real gases are chilled to very low temperatures, they exert a(n) amount of pressure in a container as compared to an ideal gas. A. greater B. equal C. lesser D. phase change 11

12 ANSWERS FOR TEACHER 1. Gases can be defined by the following statement: o All of the above Correct! The characteristics that define gases include: freely flowing to fill the container they are in, lacking a defined volume or shape, and being highly compressible. 2. The relationships between the following four variables are known as the gas laws. o pressure (P), volume (V), temperature (T), and amount (n, in moles) Correct! A gas s physical condition, or state, depends on four variables: pressure (P), volume (V), temperature (T), and amount (n, in moles). 3. Gas molecules are incredibly far apart and often interact with each other. o false Correct! It is true that gas molecules are incredibly far apart, but due to this distance the molecules rarely interact with one another. 4. The scientific principle that, so long as temperature is kept constant, the volume (V) of a fixed amount of gas is inversely proportional to its o pressure (P) is called: Boyle's Law Correct! Boyle experimented with gases by pouring mercury into a curved tube was able to then determine the volume and pressure. He found that when air is squeezed to half its original volume (V), it doubled its pressure (P). 5. The scientific principle that states that when pressure is kept constant, a fixed amount of gas increases its volume as its temperature increases is known as: o Charles's Law Correct! Charles s Law states that when pressure is kept constant, a fixed amount of gas linearly increases its volume as its temperature increases. 6. In 1811, Avogadro put forth a hypothesis stating that o Equal volumes of different gases have an equal number of molecules. Correct! Avogadro, combining ideas put forward by Dalton and Gay-Lussac, published his hypothesis in 1811 that at a gas s volume must be related to the number of its molecules. 7. Suppose you have two identical birthday balloons, with one filled with the gas helium and the other blown up by you. Assuming they re both filled to the same amount, these balloons will have the same number of molecules. o true Correct! Avogadro s law means that if we compare the number of helium molecules and the number of air molecules needed to inflate the same balloon, we would find the numbers the same. 8. When real gases are chilled to very low temperatures, they exert a(n) o amount of pressure in a container as compared to an ideal gas. lesser Correct! When a gas s temperature decreases, its molecules move slower and are less able to overcome weak intermolecular forces. This means that when a gas molecule is about to strike the wall of a container, the small attraction it experiences for nearby gas molecules reduces its impact and pressure exerted on the container. 12