Gases Flashcards
What is absolute zero?
It is the lowest temperature possible, defined as 0 K or -273.15 °C.
Can a temperature be lower than 0 K?
No, it is not possible to have a temperature lower than 0 K.
What does a temperature of 0 K mean for the particles in a substance?
The molecules in a substance have zero kinetic energy.
What is the temperature in space?
Roughly 2.7 K, just above absolute zero.
How do you convert from Celsius to Kelvin?
T (K) = θ (°C) + 273.15
How do you convert from Kelvin to Celsius?
θ (°C) = T (K) − 273.15
What does it mean that the divisions on the Celsius and Kelvin scales are equal?
A change in temperature of 1 K is equal to a change of 1 °C.
Why doesn’t Δθ in Q = mcΔθ require conversion to Kelvin?
Because the temperature difference is the same in both Celsius and Kelvin.
What is the Celsius equivalent of room temperature (300 K)?
26.85 °C.
What is Boyle’s Law?
For a constant temperature, the pressure of a gas is inversely proportional to its volume.
What is the equation for Boyle’s Law?
P₁V₁ = P₂V₂
What is Charles’s Law?
At constant pressure, the volume of a gas is proportional to its absolute temperature.
What is the equation form of Charles’s Law?
V₁/T₁ = V₂/T₂
Draw and explain a graph of pressure vs volume for Boyle’s Law.
See document for answer.
Draw and explain a graph of volume vs temperature for Charles’s Law.
See document for answer.
What is the Pressure Law?
At constant volume, pressure is proportional to absolute temperature.
What is the equation for the Pressure Law?
P₁/T₁ = P₂/T₂
Draw and explain a graph of pressure vs temperature for Pressure Law.
See document for answer.
What does pV ∝ T describe?
The relationship between pressure, volume and temperature for an ideal gas.
How do gas molecules behave in a container?
They move randomly at high speeds, collide with surfaces, and exert pressure.
How does temperature relate to molecular speed?
The hotter the gas, the faster the molecules move.
How does pressure relate to collisions?
Faster and more frequent collisions result in more force per unit area, increasing pressure.
What happens to pressure if volume decreases and temperature remains constant?
Pressure increases due to more frequent collisions.
What defines pressure in an ideal gas?
The frequency of collisions per unit area of the container.
What is the ideal gas equation?
pV = nRT
What does pV = nRT represent?
The state equation for an ideal gas, relating pressure, volume, and temperature.
What is an ideal gas?
A gas that obeys the equation of state pV = nRT at all conditions.
What is the equation for work done by a gas at constant pressure?
W = pΔV
What does W = pΔV describe?
The work done by a gas when it changes volume at constant pressure.
How is work done derived from pressure and volume?
W = F × s, where F = pA and A × s = ΔV, leading to W = pΔV.
What happens when a gas expands?
It does work on the surroundings.
What happens when a gas is compressed?
Work is done on the gas.
What is Avogadro’s constant?
6.02 × 10²³ mol⁻¹, the number of atoms in 12 g of carbon-12.
How is the mass of an atom related to atomic mass unit?
1 u ≈ mass of a proton or neutron = 1.66 × 10⁻²⁷ kg.
How many atoms are in 2.0 mol of nitrogen?
2.0 × 6.02 × 10²³ = 1.20 × 10²⁴ atoms.
How do you calculate molar mass?
It is the mass in grams of one mole of a substance, unit is g mol⁻¹.
How do you calculate moles from mass and molar mass?
n = mass / molar mass
What is the Boltzmann constant?
It relates macroscopic temperature to microscopic kinetic energy, k = R / NA.
What is the unit of Boltzmann constant?
J K⁻¹.
Why is the Boltzmann constant small?
Because a small increase in temperature causes a tiny increase in kinetic energy.
What is the difference between gas laws and kinetic theory?
Gas laws are empirical, based on observation. Kinetic theory is theoretical, based on assumptions.
What are examples of gas laws?
Boyle’s Law, Charles’s Law, Pressure Law, and the ideal gas equation.
What does the internal energy of an ideal gas depend on?
It depends only on the kinetic energy of the gas particles.
What is the relation between change in internal energy and temperature for an ideal gas?
ΔU ∝ ΔT
Define internal energy (ΔU) and its units.
ΔU = change in internal energy (Joules, J)
Define change in temperature (ΔT) and its units.
ΔT = change in temperature (Kelvin, K)
What is the effect of heating a container of gas molecules?
Molecules move faster, kinetic and internal energy increase.
Why do ideal gases have only kinetic energy?
Ideal gases assume no intermolecular forces, hence no potential energy.
What are the assumptions of kinetic theory?
Gas consists of identical molecules, perfect elastic collisions, negligible volume compared to the container, continuous random motion, obey Newton’s laws.
Time of collision is negligible compared to the time between collisions.
Very large number of molecules.
No intermolecular forces between molecules.
What is the significance of root mean square speed (crms)?
It represents the average speed of gas molecules accounting for direction.
Draw and explain the derivation of the kinetic theory of gases equation.
It is provided in the document.
What is the kinetic theory of gases equation?
pV = 1/3 Nm(crms)^2
What are the units and meanings of p, V, N, m, crms?
p = pressure (Pa), V = volume (m³), N = number of molecules, m = mass of one molecule (kg), crms = root mean square speed (m/s)
What is the kinetic theory equation in terms of density?
p = 1/3 ρ(crms)^2
What is the average kinetic energy of a molecule in an ideal gas?
Ek = (3/2)kT
What is k in the equation Ek = (3/2)kT?
k = Boltzmann constant (1.38 × 10⁻²³ J/K)
What is the relationship between kinetic energy and temperature?
Ek ∝ T
Define Brownian motion.
Random motion of small particles suspended in a fluid due to collisions with fast-moving molecules.
What does Brownian motion provide evidence for?
Existence and movement of molecules in fluids, supports kinetic theory.
Why do small molecules affect larger particles in Brownian motion?
Small molecules move faster and transfer momentum during collisions.
What is the historical significance of Democritus in gas theory?
He proposed that matter is made of indivisible atoms (atomos).
What did Robert Boyle discover?
The inverse relationship between pressure and volume at constant temperature (Boyle’s Law).
What did Amontons and Gay-Lussac discover?
The relationship between pressure and temperature at constant volume (Pressure Law).
What did Jacques Charles discover?
The relationship between volume and temperature at constant pressure (Charles’s Law).
What did Daniel Bernoulli propose?
Gases consist of particles in motion, a foundation of kinetic theory.
What was Robert Brown known for?
Discovery of Brownian motion.
What did Einstein contribute to gas theory in 1905?
Used kinetic theory to make predictions for Brownian motion, supporting atomic theory.
Why are scientific theories not accepted immediately?
They require validation through repeated experiments and peer consensus.
