[ CHEM1010 ] 7 - Gases

Gases have no constant volume and no constant shape.

What are the two specific attributes of gases regarding volume and shape?

Gases have the highest compressibility.

How does the compressibility of gases compare to other states of matter?

The gaseous state possesses the most kinetic energy.

Which state of matter possesses the most kinetic energy?

Gases have the weakest intermolecular forces.

How do the intermolecular forces in gases compare to those in solids and liquids?

The volume of the gas is equal to the volume of the container.

How is the volume of a gas determined when it is placed in a container?

1 L=10−3 m3

What is the conversion factor between 1 L and m3?

Pressure

The force exerted per unit area by gas molecules as they strike surfaces.

P = F/A

What is the mathematical formula for pressure (P) in terms of force (F) and area (A)?

High density results in high pressure, while low density results in low pressure.

How does particle density affect the pressure exerted by a gas?

Atmospheric pressure decreases as altitude increases.

What is the relationship between altitude and atmospheric pressure?

The Pascal (Pa), which equals 1 Newton per square meter.

What is the SI unit of pressure?

1 mmHg=1 torr

How many millimeters of mercury (mmHg) are equivalent to 1 torr?

14.7 psi

What is the average air pressure at sea level in pounds per square inch (psi)?

1 atm

What is the average air pressure at sea level in atmospheres (atm)?

101.325 kPa

How many kilopascals (kPa) are in 1 standard atmosphere?

A barometer.

What device is used specifically to measure atmospheric pressure?

A manometer.

What device is used to measure the pressure of gases in non-atmospheric settings?

29.92 inHg

What is the standard air pressure at sea level expressed in inches of mercury (inHg)?

K=∘C+273.15

What formula converts degrees Celsius to the Kelvin temperature scale?

They are always moving randomly.

According to Kinetic Molecular Theory, how do gas particles move?

A collision where no total kinetic energy is lost.

What is an 'elastic collision' in the context of the Kinetic Theory of Gases?

Boyle’s Law

The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure.

P1​V1​=P2​V2​

What is the formula for Boyle's Law given two sets of conditions?

A plot of Volume (V) versus 1/P.

In a plot representing Boyle's Law, what variables result in a straight line?

Charles’s Law

The volume of a fixed amount of gas at constant pressure is directly proportional to its Kelvin temperature.

V1/T1 = V2/T2

What is the mathematical equation for Charles’s Law?

Gay-Lussac’s Law

The pressure of a fixed amount of gas at constant volume is directly proportional to its Kelvin temperature.

P1/T1 = P2/T2

What is the equation representing Gay-Lussac’s Law?

Avogadro’s Law

The volume of a gas at constant temperature and pressure is directly proportional to the number of moles of the gas.

V1/n1 = V2/n2

What is the formula for Avogadro's Law?

P1V1/T1 = P2V2/T2

What is the Combined Gas Law formula?

PV=nRT

What is the Ideal Gas Law equation?

1 atm pressure and 273.15 K (0∘C).

What are the specific conditions for Standard Temperature and Pressure (STP)?

22.4 L/mol

What is the molar volume (Vm​) of an ideal gas at STP?

Standard Ambient Temperature and Pressure.

What does the acronym SATP stand for in gas chemistry?

24.465 L

What is the molar volume of a gas at SATP?

n = m/MM

How is the number of moles (n) calculated using mass (m) and molar mass (MM)?

0.0821

In the Ideal Gas Law, what is the value of the gas constant R when units are L⋅atm/(mol⋅K)?

Grams per Liter (g/L).

How is gas density generally expressed in terms of units?

d = M/22.4L/mol

What is the formula for the density of a gas at STP using its molar mass (M)?

Density is directly proportional to molar mass.

How is the density of a gas related to its molar mass?

Nitrogen is denser than Helium because its molar mass is higher.

What is the relationship between the densities of Helium (He) and Nitrogen (N2​) at STP?

Dalton’s Law of Partial Pressures

The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone.

Ptotal​=P1​+P2​+P3​+…

What is the mathematical expression for Dalton's Law?

P1​=X1​⋅Ptotal​

How is the partial pressure of a gas (P1​) calculated using its mole fraction (X1​) and total pressure (Ptotal​)?

The ratio of the number of moles of one component to the total number of moles in the mixture.

What is the definition of a mole fraction (X1​) in a gas mixture?

0.78 atm

If Nitrogen composes 78% of air, what is its partial pressure at 1.00 atm total pressure?

percent by volume

The partial pressure of a component in a gaseous mixture is equivalent to its _____ divided by 100% and multiplied by the total pressure.

High pressure, usually associated with clear weather.

In a weather map, what does the letter 'H' indicate regarding atmospheric pressure and typical weather?

Low pressure, usually associated with unstable weather.

In a weather map, what does the letter 'L' indicate regarding atmospheric pressure and typical weather?

Any three from: H2​, He, N2​, O2​, F2​, Ne, Cl2​, Ar, Kr, Xe, Rn.

List three elemental gases found at 25∘C.

Any three from: CH4​, CO2​, NH3​, SO2​, HCl, H2​S.

List three compounds that are gases at 25∘C.

independently

According to Kinetic Molecular Theory, gas particles act _____ of each other.

The volume is halved.

What happens to the volume of a gas if the pressure is doubled while temperature and moles are held constant?

The volume doubles.

What happens to the volume of a gas if the Kelvin temperature is doubled at constant pressure and moles?

gas constant

The constant of proportionality in the equation V=R⋅nT/P​ is called the _____.

By measuring the height difference (h) of the liquid in the tube.

How does a manometer indicate the pressure of a gas relative to atmospheric pressure?

1.01325 bar

What is the standard pressure value in millibars (bar)?

Because the total moles of molecules can be calculated if P, V, and T are known.

Why is it possible to treat a gas mixture, like air, as a pure substance for some calculations?

44.01 g/mol

What is the molar mass of CO2​ used in concept check calculations?

The Kelvin scale.

What temperature scale must be used in all gas law calculations?

Gay-Lussac’s Law.

In the Combined Gas Law, if volume is held constant, the equation simplifies to which law?

Decreasing pressure.

Which action results in an increase in gas volume: decreasing pressure or decreasing temperature?

The partial pressure of the water vapor.

When collecting a gas over water, what additional factor must be accounted for to find the pressure of the dry gas?

101,325 Pa

What is the average air pressure at sea level in Pascals?