gas

(noun)

A substance that can only be contained if it is fully surrounded by a container (or held together by gravitational pull); a substance whose molecules have negligible intermolecular interactions and can move freely.

Related Terms

Examples of gas in the following topics:

  • Equations of State

    • The ideal gas law is the equation of state of a hypothetical ideal gas (in which there is no molecule to molecule interaction).
    • The ideal gas law is the equation of state of a hypothetical ideal gas (an illustration is offered in ).
    • while Charles' law states that volume of a gas is proportional to the absolute temperature T of the gas at constant pressure
    • The proportionality factor is the universal gas constant, R, i.e.
    • Therefore, we derive a microscopic version of the ideal gas law

  • Gas Vesicles

    • There is a simple relationship between the diameter of the gas vesicle and pressure at which it will collapse - the wider the gas vesicle the weaker it becomes.
    • However, wider gas vesicles are more efficient.
    • They provide more buoyancy per unit of protein than narrow gas vesicles.
    • This will select for species with narrower, stronger gas vesicles.
    • Discuss the role of a gas vesicle in regards to survival

  • Density Calculations

    • The Ideal Gas Equation in the form $PV=nRT$ is an excellent tool for understanding the relationship between the pressure, volume, amount, and temperature of an ideal gas in a defined environment that can be controlled for constant volume.
    • We know the Ideal Gas Equation in the form $PV=nRT$.
    • The term $\frac{m}{V}$ appears on the right-hand side of the above rearranged Ideal Gas Law.
    • This derivation of the Ideal Gas Equation allows us to characterize the relationship between the pressure, density, and temperature of the gas sample independent of the volume the gas occupies; it also allows us to determine the density of a gas sample given its pressure and temperature, or determine the molar mass of a gas sample given its density.
    • Atmospheric science offers one plausible real-life application of the density form of the ideal gas equation.

  • Molar Mass of Gas

    • We can derive a form of the Ideal Gas Equation, PV=nRT, that incorporates the molar mass of the gas (M, $g*mol^{-1}$ ).
    • The molar mass of an ideal gas can be determined using yet another derivation of the Ideal Gas Law: $PV=nRT$.
    • We can plug this into the Ideal Gas Equation:
    • This derivation of the Ideal Gas Equation is useful in determining the molar mass of an unknown gas.
    • What is the molar mass of the gas?

  • Constant Pressure

    • For an ideal gas, this means the volume of a gas is proportional to its temperature (historically, this is called Charles' law).
    • Therefore, the work done by the gas (W) is:
    • Using the ideal gas law PV=NkT (P=const),
    • Here n is the amount of particles in a gas represented in moles.
    • $c_P = \frac{5}{2} kN_A = \frac{5}{2} R$ for a monatomic gas.

  • The Effect of the Finite Volume

    • Real gases deviate from the ideal gas law due to the finite volume occupied by individual gas particles.
    • The ideal gas law is commonly used to model the behavior of gas-phase reactions.
    • At high pressures where the volume occupied by gas molecules does not approach zero
    • The particles of a real gas do, in fact, occupy a finite, measurable volume.
    • The available volume is now represented as $V - nb$, where b is a constant that is specific to each gas.

  • Expressing the Equilibrium Constant of a Gas in Terms of Pressure

    • Take the general gas-phase reaction:
    • Recall that the ideal gas law is given by:
    • In this expression, $\Delta n$ is a measure of the change in number of moles of gas in the reaction.
    • For instance, if a reaction produces three moles of gas, and consumes two moles of gas, then $\Delta n=(3-2)=1$.
    • Write the equilibrium expression, KP, in terms of the partial pressures of a gas-phase reaction

  • The Effect of Intermolecular Forces

    • The Ideal Gas Law does not account for these interactions.
    • When the weight of individual gas molecules becomes significant, London dispersion forces, or instantaneous dipole forces, tend to increase, because as molecular weight increases, the number of electrons within each gas molecule tends to increase as well.
    • To correct for intermolecular forces between gas particles, J.D. van der Waals introduced a new term into the Ideal Gas Equation in 1873.
    • In the term above, a is a constant specific to each gas and V is the volume. van der Waals also corrected the volume term by subtracting out the excluded volume of the gas.
    • where b is the excluded volume of the gas, R is the universal gas constant, and T is the absolute temperature.

  • Basic Principles of Gas Exchange

    • Gas exchange between the air within the alveoli and the pulmonary capillaries occurs by diffusion .
    • The rate of diffusion of a gas is proportional to its partial pressure within the total gas mixture.
    • The adequacy of pulmonary gas exchange relies on the V/Q ratio (ventilation/perfusion ratio).
    • The alveoli should receive the ideal amounts of blood and gas for gas exchange.
    • Discuss how gas pressures influence the exchange of gases into and out of the body

  • Problem Solving

    • The Ideal Gas Law is the equation of state of a hypothetical ideal gas.
    • Variations of the ideal gas equation may help solving the problem easily.
    • Write down all the information that you know about the gas.
    • Remember that the general gas equation only applies if the molar quantity of the gas is fixed.
    • For example, if a gas is mixed with another gas, you may have to apply the equation separately for individual gases.