Chapter 1-6: Gas Laws, Barometry, and Dalton's Law Review

Key terms and concepts from the lecture notes on gas laws, barometry, partial pressures, mole fractions, and lab notebook practices are covered with a mix of fill-in-the-blank, vocabulary, and Q&A formats.

The instrument used to measure atmospheric pressure is a __.

Barometer

In Dalton's law, the total pressure equals the sum of the __ pressures.

partial

Mole fraction xi is defined as xi = ni / ___.

n_total

R in PV = nRT has units of __.

L atm / (mol K)

Barometer

An instrument for measuring atmospheric pressure; key tool in weather forecasting; commonly uses a mercury column.

Vacuum

A space devoid of matter; Aristotle argued against vacuums, but barometers and experiments showed vacuums can exist.

Torricelli

Italian physicist who developed the mercury barometer and linked atmospheric pressure to a column of liquid.

Mercury barometer

A barometer that uses mercury; its tall column reflects atmospheric pressure; ~76 cm Hg is a classic reference.

Pascal

Demonstrated that atmospheric pressure decreases with altitude, supporting Torricelli's model.

Open-ended manometer

A manometer with one end open to the atmosphere; liquid height difference reflects the gas–atmosphere pressure difference.

Closed-end manometer

A manometer with a vacuum or sealed end; gas pressure equals the height of the liquid column (adjusted for atmosphere if needed).

Dalton's law of partial pressures

In a gas mixture, the total pressure is the sum of the partial pressures of each component.

Partial pressure

Pressure contributed by a single gas in a mixture; Pi = xi P_total.

Mole fraction

The ratio of moles of a component to the total moles in the mixture; xi = ni / n_total.

P_total

Total pressure of a gas mixture.

n (moles)

Amount of substance measured in moles, used in PV = nRT.

Ideal Gas Law

PV = nRT; relation among pressure, volume, temperature, and amount of gas for ideal gases.

R constant

Gas constant; R = 0.08206 L·atm/(mol·K).

Molar volume

Volume per mole of gas; V_m = V / n.

Water vapor correction

When collecting gas over water, subtract the water vapor pressure from the total pressure to obtain the dry gas pressure.

Lab notebook two-column approach

Left column contains protocol/objectives; right column records data, observations, and results.

PA and PB (partial pressures)

Partial pressures of gases A and B in a mixture; Ptotal = PA + P_B (for two gases).

Pi = xi P_total

Relation between a component's partial pressure and its mole fraction in the mixture.

nA + nB = n_total

Total moles in a gas mixture equals the sum of moles of each component.

Molar volume at STP (conceptual reference)

Volume per mole of gas; used to compare gas quantities when using PV = nRT.

Assumptions when collecting gas over water

Total pressure equals the sum of the dry gas partial pressure and the water vapor pressure; subtract water vapor pressure to find the dry gas pressure.