Chemistry: Pressure, Atmospheres, and Kelvin

• Chemistry is the study of matter and its properties as well as how matter changes

Pressure

• Pressure is defined as force per unit area; it is most commonly measured in Pascals (Pa), where 1 Pa = 1 N/m².
• The Pascal (Pa) is the SI unit for pressure.
• Pressure can also be measured in atmospheres (atm), torr, and mmHg.
• The conversion factor between Pascals and atmospheres is 1 atm = 101,325 Pa.
• At sea level, atmospheric pressure is approximately 1 atm.

Atmospheres (atm) and Torr

• An atmosphere (atm) is a unit of pressure.
• 1 atm is defined as the average air pressure at sea level.
• 1 atm is equal to 760 torr.
• The torr is a unit of pressure named after Evangelista Torricelli, the inventor of the barometer.
• 1 torr is equal to 1 mmHg (millimeter of mercury).
• The conversion between atm and torr is: 1 atm = 760 torr.

Kelvin

• Kelvin (K) is the SI unit of temperature.
• The Kelvin scale is an absolute temperature scale, and 0 K is absolute zero.
• Absolute zero is the temperature at which all molecular motion stops.
• The conversion between Celsius (°C) and Kelvin (K) is: K = °C + 273.15.
• To convert from Celsius to Kelvin, add 273.15 to the Celsius temperature.
• To convert from Kelvin to Celsius, subtract 273.15 from the Kelvin temperature.

The Combined Gas Law

• The combined gas law expresses the relationship between pressure, volume, and temperature of a fixed amount of gas.
• The combined gas law equation is: (P₁V₁)/T₁ = (P₂V₂)/T₂
• P₁ = initial pressure
• V₁ = initial volume
• T₁ = initial temperature
• P₂ = final pressure
• V₂ = final volume
• T₂ = final temperature
• The combined gas law is derived from Boyle's Law, Charles's Law, and Gay-Lussac's Law.
• Boyle's Law: P₁V₁ = P₂V₂ (at constant temperature)
• Charles's Law: V₁/T₁ = V₂/T₂ (at constant pressure)
• Gay-Lussac's Law: P₁/T₁ = P₂/T₂ (at constant volume)
• The combined gas law assumes that the amount of gas remains constant.

Using Stoichiometry with the Combined Gas Law

• Stoichiometry is the calculation of quantitative relationships in chemical reactions.
• Stoichiometry can be combined with the combined gas law to solve problems involving the amount of gas produced or consumed in a reaction.
• Stoichiometry is used first to determine the number of moles of gas involved in the reaction.
• The combined gas law relates the initial and final conditions of the gas.
• The ideal gas law (PV = nRT) is often used with stoichiometry to find the volume of a gas produced or required in a chemical reaction.
• P = pressure
• V = volume
• n = number of moles
• R = ideal gas constant (0.0821 L atm / (mol K) or 8.314 J / (mol K))
• T = temperature
• Ensure that the units are consistent when using the ideal gas law (e.g., L for volume, atm for pressure, and K for temperature).

This lesson covers key concepts in chemistry, focusing on pressure measured in Pascals, atmospheres, and torr. It also explains the relationship between atmospheres and torr, and introduces the Kelvin temperature scale as an absolute temperature scale.