A barometer is an instrument that measures the pressure of the surrounding atmosphere, often with a column of mercury.
Missing Word
barometer
A barometer measures atmospheric pressure. In the classic mercury design, an inverted tube of mercury stands in a dish, and the column height rises and falls with air pressure.
Category: Gas Pressure
Question 2
The SI unit of pressure, equal to one newton per square meter, is the pascal.
Missing Word
pascal
The pascal (Pa) is the SI unit of pressure, defined as one newton of force per square meter. It is a small unit, so pressures are often given in kilopascals.
Category: Gas Pressure
Question 3
The pressure unit defined as exactly 1/760 of a standard atmosphere is the torr.
Missing Word
torr
One torr is defined as 1/760 of an atmosphere. It is very close to one millimeter of mercury, which was its original basis.
Category: Gas Pressure
Question 4
At sea level under standard conditions, air pressure supports a column of mercury 760 millimeters tall.
Missing Word
760
Standard atmospheric pressure, 1 atm, balances a mercury column about 760 mm high. This is the basis of the conversion 1 atm = 760 torr.
Category: Gas Pressure
Question 5
The gas law stating that pressure and volume are inversely proportional at constant temperature and amount is named for Robert Boyle.
Missing Word
Boyle
Boyle's law, P1V1 = P2V2, describes how a gas expands when the pressure on it drops and contracts when the pressure rises, as long as temperature and amount stay fixed.
Category: Simple Gas Laws
Question 6
The principle that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules is named for Amedeo Avogadro.
Missing Word
Avogadro
Avogadro's law follows from this principle: at constant temperature and pressure, gas volume is directly proportional to the number of moles.
Category: Simple Gas Laws
Question 7
Heating a gas from 200 K to 600 K at constant pressure and amount increases its volume by a factor of 3.
Missing Word
3
Volume is directly proportional to Kelvin temperature at constant pressure and amount (Charles's law). Since 600 K / 200 K = 3, the volume triples.
Category: Simple Gas Laws
Question 8
The absolute temperature scale required in gas law calculations is named for William Thomson, better known as Lord Kelvin.
Missing Word
Kelvin
The Kelvin scale is an absolute scale with zero at absolute zero, so for a fixed amount of gas the volume at constant pressure, and the pressure at constant volume, are directly proportional to it. It honors William Thomson, Lord Kelvin, and a Celsius temperature is converted to it by adding 273.15.
Category: Simple Gas Laws
Question 9
In the reaction of hydrogen with oxygen to form water vapor, 10 liters of hydrogen react completely with 5 liters of oxygen at the same temperature and pressure.
Missing Word
5
The balanced equation 2 H2 + O2 -> 2 H2O requires 2 volumes of hydrogen for every 1 volume of oxygen, because gas volumes at the same conditions react in the mole ratio. Half of 10 liters is 5 liters.
Category: Mixtures and Stoichiometry
Question 10
A container holds 1 mol of helium and 2 mol of neon at a total pressure of 12 atm, so the partial pressure of the helium is 4 atm.
Missing Word
4
The mole fraction of helium is 1/3, and its partial pressure is that fraction times the total: 1/3 x 12 atm = 4 atm. The neon supplies the remaining 8 atm.
Category: Mixtures and Stoichiometry
Question 11
The law stating that the total pressure of a gas mixture equals the sum of the pressures each gas would exert alone is named for John Dalton.
Missing Word
Dalton
Dalton's law of partial pressures applies to mixtures of gases that do not react. It is used, for example, to subtract water vapor pressure from the total pressure of a gas collected over water.
Category: Mixtures and Stoichiometry
Question 12
The escape of gas molecules through a tiny opening into an evacuated space is called effusion.
Missing Word
effusion
Effusion is the passage of gas through a pinhole into a vacuum, with molecules passing one at a time without colliding. Its rate is the quantity described by Graham's law.
Category: Effusion and Diffusion
Question 13
Helium, with a molar mass of 4 g/mol, escapes through a pinhole 2 times as fast as methane, with a molar mass of 16 g/mol.
Missing Word
2
The rate ratio is the square root of the inverse ratio of molar masses: the square root of 16/4 is the square root of 4, which is 2. The lighter gas escapes faster.
Category: Effusion and Diffusion
Question 14
The relationship between a gas's rate of escape through a pinhole and the inverse square root of its molar mass is named for the Scottish chemist Thomas Graham.
Missing Word
Graham
Graham's law states that rate is proportional to 1 divided by the square root of molar mass. It lets chemists compare gases or estimate an unknown molar mass from a measured rate.
Category: Effusion and Diffusion
Question 15
Kinetic-molecular theory assumes that collisions between gas molecules are elastic, meaning no kinetic energy is lost overall.
Missing Word
elastic
In an elastic collision, kinetic energy can pass from one molecule to another but the total is conserved. If collisions lost energy, a gas in an insulated container would slowly cool and its pressure would drop.
Category: Kinetic-Molecular Theory