Ideal gas pressure only takes the repulsive forces between gas molecules into consideration. The truth is, gas molecules can also exhibit attractive forces with one another (London dispersion forces). This attractive force pulls the molecules inward and slows their velocity before striking the wall of the container. As a result, real gases exert slightly less pressure compared to the ideal pressure.

use PV = nRT

V = nRT / P  ; must covert T into K

V = (2)(0.0821)(273)/ 1

= 44.8 L

At high pressure and low temperature two things are happening that will cause gases to deviate from ideal behavior.  At low temperature the individual gas molecules are moving slower. As the pressure is increased the individual molecules are being pushed closer to one another.  Thus, when the gas molecules are closer together and moving at reduced speeds they are more likely to interact with one another.  Ideal gas behavior is dependent upon an absence of intermolecular interaction between the gas molecules.  Therefore, the increased likelihood of intermolecular interactions between the gas molecules at increased pressure and decreased temperature is likely to cause gases to deviate from ideal behavior. 

Hydrogen gas is a diatomic gas, so the molecules that are filling the balloon exist as H₂.  Neon since it is a noble gas exists as a monoatomic gas, so the molecules that are filling the neon balloon exist as Ne.  The volumes given allow us to calculate the amount of each gas in moles.  At STP one mole of gas occupies 22.4 L, so there is one mole of hydrogen gas and there are two moles of neon gas.  One mole of hydrogen gas indicates that there are actually two moles of hydrogen atoms in the balloon.  Two moles of neon gas indicates that there are two moles of neon gas present in the balloon because neon exists as a monoatomic gas.  Thus there are two moles of atoms in each balloon.  

An ideal gas is most likely low concentration of identical molecules and low pressure. The molecules move randomly and collisions are completely elastic.

At STP, one mole of an ideal gas occupies 22.4L. You should know this value for the exam.

Another approach would use the ideal gas law: . Since we know that the container is at STP, we know that the container has a temperature of 273.15K and has a pressure of 1atm.

Adding the other known variables, the equation becomes

Solving for n, we find that there is 0.13 moles of hydrogen gas in the container.

One of the key charactersitics of an ideal gas is that gas molecules have no volume. This is obviously not the case, and the volume of the molecules must be added to the ideal volume. As a result, the real volume is slightly larger than the ideal volume. 

An ideal gas acts as if there are no interactions between the gaseous molecules during their rapid movements. At high temperature and low pressure the particles of the gas will not interact very much, as they will have high energy and will move around very fast. The faster the movement, the less time and contact the particles have with one another. The slower the particles are moving, the more they are starting to act like a liquid, and less like an ideal gas. High pressure will condense the particles, while low pressure will allow them to move freely. High temperature will add energy to speed the particles, while low temperature will slow them down.

We can predict the result of the heating by using the ideal gas law:

We know that , which is a constant, will never change. We also know that , the number of moles of helium inside the balloons, will stay the same since no gas is added or removed from the sealed balloons.

The variables in this case are pressure, volume, and temperature. We know that the temperature will increase because the sun is heating up the car. This leaves us with pressure and volume. Pressure will not increase because the balloons are elastic; as the gas expands, the balloons expand as well without increasing the pressure. In this scenario, only the volume will increase.

Under high pressure, the volume of the gas molecules would no longer be negligible—one of the assumptions for an ideal gas. In addition, at low temperature, the molecules would have less kinetic energy, and intermolecular forces could take affect—another assumption of an ideal gas is that there are no intermolecular attractions or repulsions.

At low pressure and high temperature, gases behave more like gases and liquids are more likely to boil (convert to gas). At high pressure and low temperature, gases behave less ideally and can condense (convert to liquid).