Chapter 3 Section 3 Notes
Bellringer The pressure of gas depends on how frequently the particles of gas strike the sides of the container holding the gas. Use your experience and, after examining each of the pairs of drawings shown below, decide whether you think the pressure of the contained gas has increased, decreased, or remained unchanged. 1.The gas in the cylinder of an automatic engine undergoes the change shown below. Does the pressure of the gas increase, decrease, or remain unchanged?
Bellringer, continued 2. The gas in the toy balloon expands outward, as shown below. After this expansion, has the pressure of the gas increased, decreased, or remained unchanged? 3. The temperature of the water vapor in the pressure cooker increases. Does the pressure of the gas increase, decrease, or remain unchanged?
Objectives Explain how gases differ from solids and liquids. State and explain the following gas laws: Boyle’s law, Charles’s law, and Gay-Lussac’s law. Describe the relationship between gas pressure, temperature and volume.
Properties of Gases Gases have unique properties. Some important properties of gases are listed below. Gases have no definite shape or volume, and they expand to completely fill their container. Gas particles move rapidly in all directions. Gases spread out easily and mix with one another. Unlike solids and liquids, gases are mostly empty space.
Properties of Gases (some important gas properties, continued) Gases have a very low density because their particles are so far apart. Because of this property, gases are used to inflate tires and balloons. Gases are compressible. Gases are fluids. Gas molecules are in constant motion, and they frequently collide with one another and with the walls of their container.
Properties of Gases Gasesexert pressure on their containers. The kinetic theory helps to explain pressure. Helium atoms in a balloon are constantly hitting each other and the walls of the balloon, as shown below. Therefore, if the balloon is punctured, the gas will escape with a lot of force, causing the balloon to pop.
Gas Laws - Boyles Boyle’s lawstates that for a fixed amount of gas at a constant temperature, the volume of the gas increases its pressure decreases. Likewise, the volume of a gas decreases as its pressure increases. Boyle’s law can be expressed mathematically as:(pressure1)(volume1) = (pressure2)(volume2) ,or P1V1 = P2V2
Boyle’s Law • At a constant TEMPERATURE: P1V1 = P2V2 where P1 = Initial Pressure V1 = Initial Volume P2 = Final (New) Pressure V2 = Final (New) Pressure
Math Skills Boyle’s Law The gas in a balloon has a volume of 7.5 L at 100 kPa. The balloon is released into the atmosphere, and the gas expands to a volume of 11 L. Assuming a constant temperature, what is the pressure on the balloon at the new volume? 1. List the given and unknown values.Given:V1 = ________ LP1 = _______ kPaV2 = ________ LUnknown: P2
2. Write the equation for Boyle’s law, and rearrange the equation to solve for P2. P1V1 = P2V2 3. Insert the known values into the equation, and solve. Math Skills, continued • P2 =68 kPa
Gas Laws - Charles Charles’s lawstates that for a fixed amount of gas at a constant pressure, the volume of the gas increases as its temperature increases. Likewise, the volume of a gas decreases as its temperature increases. As shown below, if the gas in an inflated balloon is cooled (at constant pressure), the gas will decrease in volume and cause the balloon to deflate.
Charles’s Law • At a constant PRESSURE: V1= V2 T1 T2 where V1 = Initial Volume V2 = Final Volume T1 = Initial Temperature in KELVIN (K) T2 = Final (New) Temperature in KELVIN (K) • NOTE: Temperature MUST be in KELVIN! Kelvin = _____ oC + 273 = _______ • If temperature is 25oC, then Kelvin will be?
Math Skills Charles’s Law A 250 cm3 sample of neon is collected at 44.0 oC. Assuming the pressure remains constant, what would be the volume of the neon at standard temperature, 273 K? Change temperature to Kelvin _______ oC + 273 = ________ 2. List the given and unknown values.Given:T1 = ________ KV1 = _______ cm3 T2 = ________ K Unknown: V2
2. Write the equation for Charles’s law, and rearrange the equation to solve for V2. V1T2 = V2T1 3. Insert the known values into the equation, and solve. Math Skills, continued • V2 =215 cm3
Gas Laws - Gay-Lussac’s Gay-Lussac’s lawstates that the pressure of a gas increases as the temperature increases if the volume of the gas does not change. This is why, if a pressurized container that holds gas, such as a spray can, is heated, it may explode.
G-L’s Law • At a constant PRESSURE: P1 = P2 T1 T2 where P1 = Initial Pressure T1 = Initial Temperature in KELVIN (K) P2 = Final Pressure T2 = Final (New) Temperature in KELVIN (K) • NOTE: Temperature MUST be in KELVIN!
Math Skills G-L’s Law A cylinder contain a gas which has a pressure of 125kPa at a temperature of 200 K. Find the temperature of the gas which has a pressure of 100 kPa. 1. List the given and unknown values.Given:T1 = ________ KP1 = _______ kPaP2 = ________ kPa Unknown: T2
2. Write the equation for G-L’s law, and rearrange the equation to solve for T2. P1 = P2 T1 T2 3. Insert the known values into the equation, and solve. Math Skills, continued • T2 =160 K