Graphing Relationships Learning Check Graphing Relationships Learning Check Write in your spiral whether the following slides show direct or inverse relationships.

Height of mountain Graph 1 Amount of oxygen in air

Minutes of cardiac activity Heart rate Graph 2

Word Problem The more trees that are cut down in a forest, the fewer the number of animals that can live there. Number of trees cut down increases Number of animals decreases Inverse relationship

Height of mountain Inverse Relationships As one variable increases, the other decreases. Amount of oxygen in air Inverse relationship

Minutes of cardiac activity Direct Relationship As one increases, the other increases Heart rate Direct relationship

Gases have mass. Gases seem to be weightless, but they are classified as matter, which means they have mass. The density of a gas – the mass per unit of volume – is much less than the density of a liquid or solid, however.

Gases have mass. It’s this very low density that allows us to be able to walk through the room without concerning ourselves with air resistance. Since it is so easy to “swim” across the room we don’t put much thought into the mass of a gas.

Gases can be compressed A gases low density means there to is a lot of empty space between gas molecules If you squeeze a gas (increase pressure), its volume can be reduced considerably Engine

We can use this ability of a gas to do work for us. Think of a shocks on a car. You really are riding on a pillow of air. A bump in the road compresses the gas in the shocks until the bump’s energy is absorbed.

Gases fill their containers Gases expand until they take up as much room as they possibly can. Gases spread out to fill containers until the concentration of gases is uniform (the same) throughout the entire space. This is why that nowhere around you is there an absence of air.

Gas particles are in constant random motion. Gas particles move in a straight line until they collide with other particles or the sides of the container, which causes them to change directions until they collide with something else. This bouncing off of everything around them spread the particles out until they are uniform throughout the entire container. Motion states of matter

If I opened up a bag of popcorn in front of the class you would soon be able to smell it in the back. The popcorn smell is a high energy molecule or group of molecules that is in the gas state. Gases diffuse

Gases can move through each other rapidly. The movement of one substance through another is called diffusion. Because of all of the empty space between gas molecules, another gas molecule can pass between them until each gas is spread out over the entire container. Diffusion

Gas molecules are in constant random motion they will mix with other gases uniformly (evenly). Some gases diffuse faster then other gases based on their size and their energy. Diffusion explains why we can all breath oxygen anywhere in the room. It also helps us minimize potential odoriferous problems. Gases diffuse

Gases effuse Gases can move through very small spaces in “solid” surfaces. This is called effusion. Effusion Latex balloons have small microscopic holes in them. Invisible to the human eye, but 1000 times larger than Helium atoms. The Helium atoms can escape relatively easily. Why do Mylar balloons stay inflated longer?

Gases effuse Latex balloons have small microscopic holes in them. Invisible to the human eye, but 1000 times larger than Helium atoms. The Helium atoms can escape relatively easily.

Learning Check What are the values for STP? 1 atm pressure; 0°Celsius If 142 grams of chlorine gas are in an expandable container, what volume will be occupied by the gas? 44.8 liters 1.43 g/L19.3 g/ml1.380 g/ml Which is a possible density value for a gas?

Learning Check When you pass by a pizza place and smell the pizza, what is this an example of? What property of gas is the reason you should check the firmness of an air raft before setting out onto a lake or pool? Diffusion Effusion

Gases exert pressure The sum of all of the collisions makes up the pressure the gas exerts. Gas particles exert pressure by colliding with objects in their path.

Imagine a gas in a container as a room of hard rubber balls. The collisions of the balls bouncing around exert a force on the object that with which they collide. The definition of a pressure is a force per unit area – so the total of all of the tiny collisions makes up the pressure exerted by the gas.

The gases push against the walls of their containers with a force. The pressure of gases is what keeps our tires inflated, makes our basketballs bounce, makes hairspray come out of the can, etc.

Kinetic Molecular Theory A theory used to explain the behaviors and characteristics of gases.

KMT Assumptions 1)A gas is made up of many small particles that move constantly and randomly in straight lines. 2)The molecules in a gas occupy no volume. 3)When gas molecules collide, they don’t lose energy due to friction or gain energy either. 4)Gas molecules are not attracted to each other at all. 5)The kinetic energy of gas molecules depends only on the temperature of the gas.

KMT Assumptions Ideal gases would be exactly like the description on the previous slide. It is useful to use them as a model. However, they do not actually exist. Real gases : 1)really are small, constantly moving particles 2)but, the molecules do have some volume 3)and, they do lose energy due to friction in collisions 4)and, they are slightly attracted to each other 5)their energy is really only dependent on temperature

Ideal Gas Real Gas If a Real gas is at a high temperature and low pressure, it behaves very much like an Ideal gas. At high temperatures, the molecules have a lot of energy – hard to notice really small losses and they can escape any attraction to another molecule. At low pressures, the molecules are not forced close to each other – so volume doesn’t matter and they are not close enough to be attracted very much to each other.

Gas Variables The amount (moles not volume) of a gas. The volume (in liters). The pressure The temperature

Amount (n) The quantity of gas in a given sample is expressed as moles of gas. 1 mole = molar mass = 6.02 x molecules

Volume The volume of the gas is simply the volume of the container it is contained in. The metric unit of volume is the liter (L)

Pressure The pressure of a gas is the force exerted on the wall of the container a gas is trapped in. There are several units for pressure depending on the instrument used to measure it including: Atmospheres, kiloPascals, and millimeters of Mercury

Pressure Units Atmospheres – atm kiloPascals – kPa millimeters of Mercury – mm Hg 1 atm = kPa = 760 mm Hg

Temperature The temperature of a gas is generally measured with a thermometer in Celsius. All calculations involving gases should be made after converting the Celsius to Kelvin temperature. Kelvin = C° + 273

Gas Laws Combined Gas Law PV nT PV nT The four gas variables are related through this equation.

Boyle’s Law Pressure and Volume Boyle’s Law Pressure and Volume Robert Boyle determined the relationship between pressure and volume of a gas. Moles of gas and temperature of the system were kept constant What happens to the air in a bicycle pump if you push down?

As the pressure increases Volume decreases

Boyle’s Law PV nT PV nT Moles and temperature were kept constant during the experiment.

How do Pressure and Volume of gases relate graphically? Volume Pressure PV = k Inverse relationship

Guy Lussac’s Law Pressure and Temperature Guy Lussac’s Law Pressure and Temperature Guy Lussac determined the relationship between temperature and pressure of a gas. Moles and volume were kept constant during the experiments. What happens if you heat up the gas in a closed container?

Pressure Gauge Today’s temp: 35°F Today’s temp: 85°F

Guy Lussac’s Law Pressure and Temperature Guy Lussac’s Law Pressure and Temperature PV nT PV nT Moles (n) and volume are constant

The pressure increases when temperature increases because the molecules are moving with greater speed and colliding against the sides of their containers more often. Therefore, the pressure inside that container is greater, because there are more collisions.

Temp Pressure How do Pressure and Temperature of gases relate graphically? P/T = k Direct relationshipDirect relationship

Charles’s Law Jacques Charles determined the relationship between temperature and volume of a gas. During his experiments pressure of the system and amount of gas were held constant. If you have a balloon that is beginning to deflate, what would happen if you put it in a hot car?

Volume of balloon at room temperature Volume of balloon at 5°C

Charles’s Law Volume and Temperature Charles’s Law Volume and Temperature PV nT PV nT Moles (n) and pressure are constant

Temp How do Temperature and Volume of gases relate graphically? Volume V/T = k Direct relationship

Ideal Gas Law PV nT PV nT At STP, 1 mole of gas will take up 22.4 L of the volume of the container

Ideal Gas Law (1atm) (22.4L) (1mole)(273K) PV nT Substitute these values for one side of the equation.

Ideal Gas Law atm ∙L mole∙K PV nT Calculate; this is the Gas Constant. Take a careful look at the units. R0.082

Ideal Gas Law PVnT Rearrange. This is the form most commonly used. Use the Ideal Gas Equation to solve a problem when the amount (moles)of gas is given R

At constant volume and temp., the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures. P total = P 1 + P 2 + P