gases have unique properties. some important properties of gases are listed below
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• 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.
Chapter 14 Section 3 Behavior of Gases
Important Properties of Gases, 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 – these collisions create pressure
Chapter 14 Section 3 Behavior of Gases
Properties of Gases, continued
• Gases exert 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.
Chapter 14 Section 3 Behavior of Gases
Factors that Affect Gas Pressure - include its temperature, its volume, and the number of particles within it.
TEMPERATURE• Raising the temperature of a gas will increase its
pressure if the volume of the gas and the number of particles are constant.
• Increasing the speed of the particles but keeping the space available to move the same causes the number of collisions to increase.
• This is visible when the gas in tires heats up due to highway or NASCAR driving, potentially causing the tire to explode due to increased pressure.
Section 3 Behavior of GasesChapter 14
VOLUME
• Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles in the gas remain constant.
• The gas moves at the same speed but within the confines of a smaller space causing a greater number of collisions.
• The pressure – volume relationship of gases allows inhaling and exhaling in our breathing process to occur.
Section 3 Behavior of GasesChapter 14
NUMBER OF PARTICLES
• Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant.
• Adding more air into inflated tires becomes increasingly difficult to impossible after the tire’s internal pressure is at maximum.
Section 3 Behavior of GasesChapter 14
Gas Laws
• Boyle’s law states 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
Chapter 14 Section 3 Behavior of Gases
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?
Chapter 14 Section 3 Behavior of Gases
Gas Laws, continued• Charles’s law states 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 decreases.
• 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.
Chapter 14 Section 3 Behavior of Gases
Gas Laws, continued
• The equation for Charles’s law is
V1 = V2, the volume of a gas is directly
T1 T2 proportional to its absolute temperature
• Absolute temperature is the Kelvin temperature.
K = oC + 273.15 There are no values below
zero on this scale.
Section 3 Behavior of GasesChapter 14
Gas Laws, continued
• Gay-Lussac’s law states 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.
Chapter 14 Section 3 Behavior of Gases
Gas Laws, continued
The Combined Gas Law• The relationships described in Boyle’s law, Charles’s
law, and Gay-Lussac’s laws can be summarized into one law. This is the combined gas law.
• The equation for the combined gas law is
P1. V1 = P2 . V2
T1 T2
• Recall that temperature must be in the Kelvin scale.
Section 3 Behavior of GasesChapter 14
Gas Laws, continued
Problem: A cylinder that contains air at a pressure of 100 kPa has a volume of 0.75 L. The pressure is increased to 300 kPa. The temperature does not change. Find its new volume of air.
Solution: • Initial pressure = 100 kPa, Initial volume = 0.75 kPa• Final pressure = 300 kPa, Final volume = unknown• Temperature is unchanged.
Section 3 Behavior of GasesChapter 14
• Adjust the combined gas law formula by omitting the temperatures leaving - P1V1 = P2V2
• Solve for the unknown variable, leaving –
V2 = P1V1
P2
• Replace variables with numbers and solve the unit:
V2 = (100 kPa)(0.75 L) = 0.25 L
300 kPa• Check answer for credibility.
Section 3 Behavior of GasesChapter 14
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