Gases Chapter 8 Chapter 8
8.1 - Properties of Gases 8.2 – Pressure and Volume (Boyle’s Law) 8.3 – Temperature and Volume (Charles’ Law) 8.4 – Temperature and Pressure (Guy-Lussac’s Law) 8.5 – The Combined Gas Low 8.6 – Volume and Moles (Avogadro’s Law) 8.7 – The Ideal Gas Law 8.8 – Partial Pressures (Dalton’s Law) 8.1 Properties of Gases Goal: Describe the Kinetic Molecular Theory of Gases and the units of measurement used for gases. Gases
We are surrounded by gases, but we are often unaware of their presence.
Of the elements on the periodic table, only a handful
are gases at room temperature: H2, He, N2, O2, F2, Cl2, and the noble gases.
Other common gases are molecules with oxygen and
small nonmetals: CO, CO2, NO, NO2, SO2, SO3
Generally, molecules that are gases at room temperature have fewer than 5 atoms and are from the 1st and 2nd period. Gases
The behavior of gases is quite different from that of liquids and solids.
× Gas particles are far apart, whereas particle of both liquids an solids are held close together.
× A gas has no definite shape or volume and will completely fill any container.
× Because there are great distances between gas particles, a gas is less dense than a solid or liquid and easy to compress. Kinetic Molecular Theory of Gases
1. A gas consists of 2. The attractive 3. The actual volume small particles (atoms forces between the occupied by gas or molecules) that particles of a gas are molecules is move randomly with usually very small. extremely small high velocities. compared with the Gas particles are far volume that the gas Gas molecules apart and fil a occupies. moving in random container of any size directions at high and shape. The volume of the speeds cause a gas to gas is considered fill the entire volume equal to the volume of a container. of the container.
Most of the volume of a gas is empty space, which allows gases to be easily compressed. Kinetic Molecular Theory of Gases
4. Gas particles are in constant 5. The average kinetic energy of motion, moving rapidly in gas molecules is proportional to straight paths. the temperature in Kelvin.
When gas particles collide, they Gas molecules move faster as rebound and travel in new the temperature increases. directions. At higher temperatures, gas Every time they hit the walls of molecules hit the walls of the the container they exert container more often and with pressure. more force, producing higher pressures. An increase in the number or force of collisions against the walls of the container causes an increase in the pressure of the gas. Applications
The kinetic molecular theory helps explain everyday things:
Smells Explosions We can quickly smell Sometimes tires or gas- perfume when a bottle is filled containers explode opened across the room when temperatures are too because its particles move high. rapidly in all directions. From the KMT, we know At room temp, air molecules that gas particles move move at 1000 mph. faster when heated, hit the walls of a container with more force, and cause a buildup of pressure inside a container. When we talk about a gas, we describe it in terms of 4 properties: Pressure Volume Temperature Amount Pressure (P)
Gas molecules are Common units: extremely small and move × atmospheres (atm) rapidly. × mm of mercury When they hit the walls of (mmHg) a container, they exert pressure. × in of mercury (inHg)
If we heat the container, × Pascals (Pa) the molecules move faster and smash into the walls × torr more often and with increased force, thus × pounds per square increasing the pressure. inch (psi) Volume, Temperature, Amount
Volume (V) Temperature (T) Amount of gas (n)
The volume of a gas The temperature of The amount of gas equals the size of a gas is related to refers to the mass of the container in the kinetic energy of the gas present. which the gas is its particles. placed. Units: grams or Kinetic Energy – moles Units: L, mL energy of motion. As particles move (moles are used in faster, they equations) generate more kinetic energy in the form of heat.
Units: Kelvin (no negative numbers) 12 13 Convert 4820 mmHg to atmospheres. (1 atm = 760 mmHg) Convert 48 psi to torr (14.7 psi = 1 atm = 760 mmHg) Chapter 8
8.1 - Properties of Gases 8.2 – Pressure and Volume (Boyle’s Law) 8.3 – Temperature and Volume (Charles’ Law) 8.4 – Temperature and Pressure (Guy-Lussac’s Law) 8.5 – The Combined Gas Low 8.6 – Volume and Moles (Avogadro’s Law) 8.7 – The Ideal Gas Law 8.8 – Partial Pressures (Dalton’s Law) 8.2 Pressure and Volume (Boyle’s Law)
Goal: Use the pressure-volume relationship (Boyle’s Law) to determine the final pressure or volume when the temperature and amount of gas are constant. Pressure and Volume Imagine that you can see air particles hitting the walls inside a bicycle tire pump.
What happens to the pressure inside the pump as you push down on the handle?
As the volume decreases, the air molecules are crowded together. More collisions occur with the walls, increasing the pressure. P and V – Inverse Relationship
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When a change in one property causes a change in another, the two properties are said to be related.
If the changes occur in opposite directions, the properties are inversely related.
The inverse relationship between P and V is known as Boyle’s Law. P and V – Boyle’s Law
Boyle’s Law: the volume (V) of a sample of a gas changes inversely with the pressure (P) of the gas as long as there is no change in the temperature (T) or amount of gas (n)
A result of Boyle’s Law is the equation:
P1V1 = P2V2
P1 = initial pressure P2 = final pressure
V1 = initial volume V2 = final volume The pressure inside a tire pump is 1.4 atm at 3.0 L. If the volume is decreased to 2.0 L, what is the new air pressure? A bubble of natural gas (CH4) has a volume of 45.0 mL at 1.60 atm of pressure when underground. What volume will the bubble have it if reaches Earth’s surface where atmospheric pressure is 744 mmHg? Assume no change in temperature or amount of gas. (760 mmHg = 1 atm) FYI – PV relationship in Breathing
The importance of Boyle’s Law is shown in the mechanics of breathing.
Our lungs are elastic, balloon-like structures contained in an airtight chamber called the thoracic cavity. The diaphragm, a muscle, forms the flexible floor of the cavity. FYI – PV relationship in Breathing
Inhalation (Inspiration) The process of taking a breath begins when the diaphragm contracts, causing an increase in the volume of the lungs. According to Boyle’s Law, this causes pressure in the lungs to decrease.
The pressure of the lungs drop below the atmospheric pressure creating a pressure gradient between the lungs and atmosphere.
Air molecules flow from higher pressure to lower and you breathe in. FYI – PV relationship in Breathing
Exhalation (Expiration) occurs when the diaphragm relaxes and moves back up into the thoracic cavity. The volume of the thoracic cavity and lungs decrease, causing an increase in the pressure in the lungs.
Now the pressure in the lungs in higher than the pressure of the atmosphere and a new pressure gradient causes the air molecules to flow out of the lungs. Chapter 8
8.1 - Properties of Gases 8.2 – Pressure and Volume (Boyle’s Law) 8.3 – Temperature and Volume (Charles’ Law) 8.4 – Temperature and Pressure (Guy-Lussac’s Law) 8.5 – The Combined Gas Low 8.6 – Volume and Moles (Avogadro’s Law) 8.7 – The Ideal Gas Law 8.8 – Partial Pressures (Dalton’s Law) 8.3 Temperature and Volume (Charles’ Law)
Goal: Use the temperature-volume relationship (Charles’ Law) to determine the final temperature or volume when the pressure and amount of gas are constant. Hot air balloons…
You are going to take a ride in a hot air balloon. The captain turns on a propane burner to heat the air inside the balloon. As the air is heated, it expands and becomes less dense than the air outside, causing the balloon to rise… Charles’ Law
In 1787, Jacques Charles, a balloonist and physicist, proposed that the volume of a gas is directly related to temperature.
Charles’ Law: The volume (V) of a gas is directly related to the temperature (T) when there is no change in the pressure (P) or amount (n) of gas.
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29 Charles’ Law