# What is the relationship between gas particles and pressure

### CH Lesson 1 - Gas Laws

Jan 7, Gas particles spread out to fill a container evenly, unlike solids and is held constant, volume and pressure have an inverse relationship; that. Early scientists explored the relationships among the pressure of a gas (P) and its the volume of the gas decreases because the gas particles are forced closer . It is these collisions between the particles of the gas and the walls of the container it The relationship of a gas with pressure and volume was developed by the.

The particles exert more force on the interior volume of the container. This force is called pressure.

There are several units used to express pressure. Some of the most common are atmospheres atmpounds per square inch psimillimeters of mercury mmHg and pascals Pa.

The units relate to one another this way: Besides pressure, denoted in equations as P, gases have other measurable properties: In work involving gas temperature, the Kelvin scale is often used. Because temperature and pressure vary from place to place, scientists use a standard reference point, called standard temperature and pressure STPin calculations and equations.

Standard temperature is the freezing point of water — 32 degrees Fahrenheit 0 degrees Celsius, or Standard pressure is one atmosphere atm — the pressure exerted by the atmosphere on Earth at sea level.

### Lecture 9: Gases

Gas laws Temperature, pressure, amount and volume of a gas are interdependent, and many scientists have developed laws to describe the relationships among them. Boyle's law Boyle's law is named after Robert Boyle, who first stated it in Boyle's law states that if temperature is held constant, volume and pressure have an inverse relationship; that is, as volume increases, pressure decreases, according to the University of California, Davis' ChemWiki.

TDD Lesson 1: Gas Laws In this section, we'll examine how n, V, T, and P are related to each other and how they affect each other. These gas laws will form the basis for the Ideal Gas Law, which we'll study in the next section.

Imagine it contains 2 moles of gas and the pressure is torr. What do you think would happen to the pressure if we added another 2 moles of gas?

**Pressure, Volume and Temperature Relationships**

Since pressure is due to collisions with the walls of the container, you should think about how doubling the number of gas particles from 2 to 4 moles will affect the number and force of the collisions in the container. How will doubling the number of gas particles change the number of collisions that occur each second?

How will doubling the number of gas particles change the force with which the average particle collides with the wall? The Kinetic Molecular Theory KMT says that the pressure is due to collisions with the walls of the container and depends on how many gas particles there are and how violent the collisions are. Doubling the number of gas particles has no effect on how hard they strike the walls of the container. That force is determined by the velocity and mass of the particles.

Doubling the number of gas particles does exactly double the number of times each second a particle strikes the wall of the container. Thus the pressure doubles as well. For an ideal gas, the pressure is directly proportional to the number of moles of gas present. In mathematical symbols, we say that P is equal to a constant times n.

The value of the constant depends on the volume and the temperature. The fact that P and n are directly proportional means not just that when n increases so does P, it means that when n is doubled, so is P; when n is tripled, so is P; when n is cut by one fourth, so is P. In general, when n increases or decreases, the ratio of the new to the old values of n will be the same as the ratio of the new to the old values of P. The value of the constant k determines how large P is compared to n, but no matter what value k has, large or small, the correspondence between the ratio of the change in n and the ratio of the change in P will exist.

What will happen to the pressure? Again, consider how the number of collisions and the force of the average collision will be affected.

As before, since we have not changed the temperature, the force of the average collision will not change. Again, because the temperature has not changed, the collisions will be no more or less violent, but the number of collisions will change. In one third the volume, each gas particle has, on the average, one third the distance to go before hitting the wall of the container, and will therefore do so three times as often, increasing the pressure by a factor of three.

For an ideal gas, the pressure is inversely proportional to the volume of the container.

## Lesson 1: Gas Laws

Mathematically, we can express this by saying that the pressure is equal to a constant times one over the volume or that the pressure times the volume equals a constant. This time, the value of the constant depends on the temperature and the number of moles. Inverse proportionality works the same way that direct proportionality does, except that when two quantities are inversely proportional, when one goes up, the other goes down.

The correspondence between ratios remains. When one goes up by a factor of two, the other goes down by a factor of two, and so on. Again, the constant determines the relative size of the two quantities. If the constant is close to 1, they will be close to the same size. If the constant is very large or very small, one will be much larger or much smaller than the other.

You can experience this relationship yourself in the lab. In the area labeled Exercise 9 you will find a syringe filled with a gas. The opening has been closed off so that you can change the volume of the syringe without changing the amount of gas present.

When you start, the pressure inside the syringe is the same as the pressure outside the syringe. See what happens as you decrease and increase the volume occupied by the gas inside the syringe.

## Properties of Matter: Gases

The pressure of the surrounding air does not seem like much. To get an idea of how strong it is, see how much work it takes to cut the volume of the syringe in half and hold it there.

If you cut the volume of the syringe in half, you will double the pressure inside and the additional pressure you will be working against will be the difference between the pressure inside the syringe 2 atm and outside the syringe 1 atm: If you increase the volume of the syringe by a factor of two, the pressure inside the syringe will drop to 0. What would happen to the pressure if you increased the temperature from K to K?

Also same as before, initial and final volumes and temperatures under constant pressure can be calculated. The Pressure Temperature Law This law states that the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature. P Same as before, a constant can be put in: The Volume Amount Law Amedeo Avogadro Gives the relationship between volume and amount when pressure and temperature are held constant.

Remember amount is measured in moles. Also, since volume is one of the variables, that means the container holding the gas is flexible in some way and can expand or contract. If the amount of gas in a container is increased, the volume increases.

### Kinetic Molecular Theory

If the amount of gas in a container is decreased, the volume decreases. V As before, a constant can be put in: The Combined Gas Law Now we can combine everything we have into one proportion: The volume of a given amount of gas is proportional to the ratio of its Kelvin temperature and its pressure.

Same as before, a constant can be put in: The Ideal Gas Law The previous laws all assume that the gas being measured is an ideal gas, a gas that obeys them all exactly.