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ghostanime2001

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In summary, the conversation discusses the concept of constants in relation to the three gas laws (Boyle's Law, Charles' Law, and Avogadro's Law) and the ideal gas law. Constants are properties that remain unchanged in an experiment, such as the molecular weight of a gas, and are important in understanding the relationships expressed through the gas laws. The ideal gas law, PV = nRT, shows the interaction between the variables of pressure, volume, temperature, and number of moles. By changing one variable, the others are affected, but the product of the four variables remains constant. This concept is important in designing experiments and understanding the mathematics behind the gas laws.

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ghostanime2001

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Chemistry news on Phys.org

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Studiot

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Gasses have a number of interdependent mechanical and thermal properties that are set by circumstances. That is they depend upon both the external world and the gas itself.

These properties include the temperature (T) the pressure (P) and the volume (V) and density (ρ)

There are also properties which are inherent in the particular sample of gas itself and not dependent on the external world.

These include the mass (m), molecular weight (M), number of moles (n), and so on. Some of these will be constant eg the molecular weight of oxygen is a fixed number, 32.

Over the centuries, various individual laws linking all these properties have been developed and these are what you ar now studying.

Important ones are

Boyles Law, Charles, Law, Avogadro's Law, the ideal gas law which is a combination of Boyles and Charles laws.

Taking the last one.

PV = nRT

One variable, number of moles, is set by the sample of gas itself

n = number of moles = mass / molecular weight.

By changing the environment we can change or fix the other three variables, P, V and T.

However we do not have total freedom to set all three. They interact so that changing one changes at least one of the others.

The equation describes this interaction.

So if we have a balloon of gas and heat it up (raise the temperature) it expands. That is the volume increases.

However we have not heated the whole atmosphere around the balloon so we have not changed the pressure upon it.

The equation tells us that if we double the temperature we must multiply the other side by 2 to compensate ie double the volume.

Alternatively we could heat the same amount of gas in a rigid container (pressure vessel).

And yes, you guessed it, we have now held the volume constant so the factor of 2 is now applied to the pressure, which must therefore double.

Does this help?

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ghostanime2001

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Studiot

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If, however, they remain unchanged when we change the circumstances from state1 to state2, then the diffeerence or change = 0

That is in our rigid container if V

Then ΔV = V

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Borek

Mentor

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For every sample of the ideal gas [itex]\frac{PV}{nT}[/itex] has exactly the same value. That means when preparing a gas sample you have only a limited number of degrees of freedom - you can select any three parameters, but the fourth one will be a function of these three. [itex]\frac{PV}{nT}[/itex] is a constant.

In other cases we are limiting number of parameters we change. For example when we say PV=const we mean - if we keep nT constant (for example we can do experiments without allowing gas to escape nor enter the vessel, and we allow it to have the same temperature all the time), PV is a constant as well. Or when we say [itex]\frac V T = const[/itex] we mean it is constant as long as [itex]\frac P n[/itex] doesn't change (again, many ways to design an experiment this way).

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ghostanime2001

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- #7

Borek

Mentor

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PV=k

You measure P, V and calculate the product. Then you change pressure, measure P, V - and product stays the same.

The three main variables in gas laws are pressure (P), volume (V), and temperature (T). These variables are interdependent and can be manipulated to determine the behavior of gases.

According to Boyle's law, pressure and volume are inversely proportional in a closed system at a constant temperature. This means that as pressure increases, volume decreases and vice versa.

The ideal gas law (PV = nRT) is a combination of Boyle's law, Charles's law, and Avogadro's law. It is used to calculate the unknown variable (P, V, T, or n) in a gas system, given the values of the other variables.

According to Charles's law, volume and temperature are directly proportional in a closed system at a constant pressure. This means that as temperature increases, volume also increases and vice versa.

Gas laws can be applied in various real-world situations, such as determining the amount of gas needed for a specific reaction or understanding the behavior of gases in weather patterns. They are also used in industries such as chemistry, engineering, and meteorology.

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