Why gases can be compressed

Water is the only common substance that is found as a solid, liquid and gas. All three states of water can be seen in this photo. Because ice is less dense than water, ice floats. In Antarctica the sea ice is thick enough in places to drive on and even land planes. Water vapour is invisible and can only be seen when it cools and condenses into clouds or water droplets on cold surfaces. Think about the importance of water being denser than ice; what would happen if ice was denser than water?

Skip to main content. Listen to this page. Water is the only common substance that is naturally found as a solid, liquid or gas. Solids, liquids and gases are known as states of matter.

What is matter? Scientists use the word matter to describe anything that takes up space and has mass. Matter is made up of tiny particles, including; atoms and groups of atoms called molecules Atoms are like individual LEGO blocks. How are atoms arranged in minerals? Which has a bigger volume solid, liquid or gas?

What type of substance doesn't have a consistent volume: liquid, solid, or gas? See all questions in Properties of Solids, Liquids, and Gases. Impact of this question views around the world. In other words, gases expand to fill any container. When restricted by forces, they exert pressure in opposition to those forces.

Compressing a gas increases its pressure. So does heating it, even when volume remains constant. Regardless of current pressure, compressing a gas is easier than compressing solids or liquids. Increase in temperature produces increase in pressure. Watch the video at the link below and answer the following questions:. How important is it to check the weather? Each day, hundreds of weather balloons are launched.

Made of a synthetic rubber and carrying a box of instruments, the helium-filled balloon rises up into the sky. As it gains altitude, the atmospheric pressure becomes less and the balloon expands. At some point the balloon bursts due to the expansion, the instruments drop aided by a parachute to be retrieved and studied for information about the weather.

Robert Boyle , an English chemist, is widely considered to be one of the founders of the modern experimental science of chemistry. He discovered that doubling the pressure of an enclosed sample of gas while keeping its temperature constant caused the volume of the gas to be reduced by half. An inverse relationship is described in this way. As one variable increases in value, the other variable decreases. Physically, what is happening? The gas molecules are moving and are a certain distance apart from one another.

An increase in pressure pushes the molecules closer together, reducing the volume. If the pressure is decreased, the gases are free to move about in a larger volume. The is a constant for a given sample of gas and depends only on the mass of the gas and the temperature.

The Table below shows pressure and volume data for a set amount of gas at a constant temperature. The third column represents the value of the constant for this data and is always equal to the pressure multiplied by the volume. As one of the variables changes, the other changes in such a way that the product of always remains the same.

Volume is plotted on the -axis, with the corresponding pressure on the -axis. We use and to stand for the initial pressure and initial volume of a gas. After a change has been made, and stand for the final pressure and volume. This equation can be used to calculate any one of the four quantities if the other three are known.

A sample of oxygen gas has a volume of mL when the pressure is equal to kPa. The gas is allowed to expand into a 1. Calculate the new pressure of the gas. Step 1: List the known quantities and plan the problem. It is important that the two volumes and are expressed in the same units, so has been converted to mL. First, rearrange the equation algebraically to solve for.

Now substitute the known quantities into the equation and solve. Step 3: Think about your result. The volume has increased to slightly over 4 times its original value and so the pressure is decreased by about. The pressure is in kPa and the value has three significant figures. Note that any pressure or volume units can be used as long as they are consistent throughout the problem.

How do you bake bread? Everybody enjoys the smell and taste of freshly-baked bread. It is light and fluffy as a result of the action of yeast on sugar. The yeast converts the sugar to carbon dioxide, which at high temperatures causes the dough to expand. The end-result is an enjoyable treat, especially when covered with melted butter. As a container of confined gas is heated, its molecules increase in kinetic energy and push the movable piston outward, resulting in an increase in volume.

French physicist Jacques Charles studied the effect of temperature on the volume of a gas at constant pressure. The absolute temperature is temperature measured with the Kelvin scale. The Kelvin scale must be used because zero on the Kelvin scale corresponds to a complete stoppage of molecular motion. The Table below shows temperature and volume data for a set amount of gas at a constant pressure. The third column is the constant for this particular data set and is always equal to the volume divided by the Kelvin temperature.

When this data is graphed, the result is a straight line, indicative of a direct relationship, shown in Figure below. The volume of a gas increases as the Kelvin temperature increases. Notice that the line goes exactly toward the origin, meaning that as the absolute temperature of the gas approaches zero, its volume approaches zero. However, when a gas is brought to extremely cold temperatures, its molecules would eventually condense into the liquid state before reaching absolute zero.

The temperature at which this change into the liquid state occurs varies for different gases. Now we use and to stand for the initial volume and temperature of a gas, while and stand for the final volume and temperature. The direct relationship will only hold if the temperatures are expressed in Kelvin.

Temperatures in Celsius will not work. A balloon is filled to a volume of 2. Find the new volume of the balloon. The temperatures have first been converted to Kelvin. The volume increases as the temperature increases.

The result has three significant figures. Perform the calculations at the web site below:. How much propane is in the tank? Propane tanks are widely used with barbeque grills. You can buy gauges that measure the pressure inside the tank to see how much is left. The gauge measures pressure and will register a higher pressure on a hot day than it will on a cold day. So you need to take the air temperature into account when you decide whether or not to refill the tank before your next cook-out.

When the temperature of a sample of gas in a rigid container is increased, the pressure of the gas increases as well. The increase in kinetic energy results in the molecules of gas striking the walls of the container with more force, resulting in a greater pressure.

The French chemist Joseph Gay-Lussac discovered the relationship between the pressure of a gas and its absolute temperature. A graph of pressure vs. As a gas is cooled at constant volume its pressure continually decreases until the gas condenses to a liquid.

The gas in an aerosol can is under a pressure of 3. It is dangerous to dispose of an aerosol can by incineration. The pressure increases dramatically due to large increase in temperature. Work on the problems found at the web site below:. What keeps things cold? The modern refrigerator takes advantage of the gas laws to remove heat from a system. Compressed gas in the coils see above is allowed to expand. This expansion lowers the temperature of the gas and transfers heat energy from the material in the refrigerator to the gas.

As the gas is pumped through the coils, the pressure on the gas compresses it and raises the gas temperature. This heat is then dissipated through the coils into the outside air. As the compressed gas is pumped through the system again, the process repeats itself.

To this point, we have examined the relationships between any two of the variables of , , and , while the third variable is held constant. However, situations arise where all three variables change.

The combined gas law expresses the relationship between the pressure, volume, and absolute temperature of a fixed amount of gas. For a combined gas law problem, only the amount of gas is held constant. What will be the new gas volume? Use the combined gas law to solve for the unknown volume. STP is K and 1 atm. The temperatures have been converted to Kelvin. Both the increase in pressure and the decrease in temperature cause the volume of the gas sample to decrease. Since both changes are relatively small, the volume does not decrease dramatically.

It may seem challenging to remember all the different gas laws introduced so far. For example, consider a situation where a change occurs in the volume and pressure of a gas while the temperature is being held constant. In that case, it can be said that. Look at the combined gas law and cancel the variable out from both sides of the equation.

Work on the problems at the link below:. How much air do you put into a tire? A flat tire is not very useful. It does not cushion the rim of the wheel and creates a very uncomfortable ride. When air is added to the tire, the pressure increases as more molecules of gas are forced into the rigid tire.

How much air should be put into a tire depends on the pressure rating for that tire. Too little pressure and the tire will not hold its shape.