# Pressure and number of moles relationship advice

### Relationships among Pressure, Temperature, Volume, and Amount Gives the relationship between volume and amount when pressure when you have change in moles of gas, the volume increases/decreases. Early scientists explored the relationships among the pressure of a gas (P) . the volume of a sample of gas is directly proportional to the number of moles of gas. The volume of a mole of gas is inversely proportional to the pressure and directly proportional to the temperature, i.e. 4 in your list of answers.

And while one little particle collision might not have a huge amount of pressure, when you think about the huge amount of particles and the huge number of collisions, we pretty easily get enough pressure to fill the balloon. And the neat thing about balloons is we typically don't just fill them up a little bit, we can fill them up a lot. And the more we fill them up the tauter the sides get, indicating that they have more pressure.

So what might cause the pressure to increase? Well, according to our little pressure formula here, pressure is directly proportional to the force. So let's think about what would cause the force to increase.

We know that force is equal to the mass times acceleration. So if we increase the magnitude of the acceleration, we can increase the force. Because force and acceleration are also directly proportional. That means if we have a greater change in velocity- because that's what acceleration is, it's a change in velocity. So if we have a greater change in velocity during the collision, we can increase the force. And that means that the faster our little particles are moving, the greater the force.

And thus the greater the pressure. And if you remember from our last video, we said that temperature was a measure of the average kinetic energy of the particles.

So really what we're saying, is that when we increase the temperature, we're increasing the pressure that the gas exerts. So what else might cause the pressure to increase? Well, if the total pressure is the sum of those little individual collisions, more collisions would mean more pressure. But how do we increase the number of collisions? One method might be to add more particles, because more particles means more collisions.

## 6.3: Relationships among Pressure, Temperature, Volume, and Amount

So more moles of gas- remember that moles is simply referring to the number of particles. More moles of gas means more pressure. Now we could also increase the frequency of these collisions by making the container smaller. Because the particles would have less space to move around, and would therefore hit the sides of the container more frequently.

So if we decrease the volume- If we decrease the space of the container, we're going to increase the pressure. So we can change the pressure of a gas. But how do we measure those changes?

## Pressure and the simple mercury barometer

Well, a long time ago in a former student of Galileo named Evangelista Torricelli asked the same question while he was trying to measure the changing pressure of the gas in our atmosphere. And he solved the problem by inventing the Torricellian Barometer. A barometer is a device that measures pressure.

And so he took a glass tube, and he filled it up with mercury. So he took a glass tube and he filled it up with mercury.

And he quickly flipped the tube over, and he stuck the open end into an open dish of mercury. So he stuck the tube into an open dish of mercury, open end down, and interestingly enough, most of the mercury stayed in the tube.

And the mercury stayed in the tube, even though it was trying to flow out, because as it tries to flow out it exerts a pressure on the mercury in the dish, which then causes the mercury in the dish to push upward against the air. And when the pressure of the rising mercury meets the pressure of the atmosphere pushing down on the liquid's surface, the mercury that's in the tube, it can't flow anymore.

The history of their discoveries provides several excellent examples of the scientific method. The Relationship between Pressure and Volume: Boyle's Law As the pressure on a gas increases, the volume of the gas decreases because the gas particles are forced closer together. Conversely, as the pressure on a gas decreases, the gas volume increases because the gas particles can now move farther apart.

Weather balloons get larger as they rise through the atmosphere to regions of lower pressure because the volume of the gas has increased; that is, the atmospheric gas exerts less pressure on the surface of the balloon, so the interior gas expands until the internal and external pressures are equal.

The Irish chemist Robert Boyle — carried out some of the earliest experiments that determined the quantitative relationship between the pressure and the volume of a gas. Boyle used a J-shaped tube partially filled with mercury, as shown in Figure 6. In these experiments, a small amount of a gas or air is trapped above the mercury column, and its volume is measured at atmospheric pressure and constant temperature. More mercury is then poured into the open arm to increase the pressure on the gas sample. The pressure on the gas is atmospheric pressure plus the difference in the heights of the mercury columns, and the resulting volume is measured. This process is repeated until either there is no more room in the open arm or the volume of the gas is too small to be measured accurately.

### Volume and Moles of Gas by dailyn collins on Prezi

This relationship between the two quantities is described as follows: Dividing both sides of Equation 6. The numerical value of the constant depends on the amount of gas used in the experiment and on the temperature at which the experiments are carried out.

At constant temperature, the volume of a fixed amount of a gas is inversely proportional to its pressure. Boyle used non-SI units to measure the volume in. Hg rather than mmHg. Because PV is a constant, decreasing the pressure by a factor of two results in a twofold increase in volume and vice versa.

The Relationship between Temperature and Volume: Charles's Law Hot air rises, which is why hot-air balloons ascend through the atmosphere and why warm air collects near the ceiling and cooler air collects at ground level. Because of this behavior, heating registers are placed on or near the floor, and vents for air-conditioning are placed on or near the ceiling.