UPCAT Chemistry — Gas Laws & ThermochemistryFlash Cards

State Boyle's Law and provide its mathematical equation.

Boyle's Law: At constant temperature, the pressure and volume of a gas are inversely proportional. When pressure increases, volume decreases. Formula: P₁V₁ = P₂V₂. Example: If pressure doubles, volume is halved.

A gas occupies 2.0 L at 1.0 atm pressure. What volume will it occupy at 3.0 atm (temperature constant)?

Using Boyle's Law: P₁V₁ = P₂V₂ Given: P₁ = 1.0 atm, V₁ = 2.0 L, P₂ = 3.0 atm Step 1: V₂ = P₁V₁/P₂ Step 2: V₂ = (1.0)(2.0)/3.0 = 0.67 L Answer: 0.67 L

State Charles's Law and its mathematical relationship.

Charles's Law: At constant pressure, the volume and temperature of a gas are directly proportional. When temperature increases, volume increases. Formula: V₁/T₁ = V₂/T₂. Temperature must be in Kelvin!

A gas has volume 1.5 L at 25°C. What volume at 100°C (pressure constant)?

Using Charles's Law: V₁/T₁ = V₂/T₂ Step 1: Convert to Kelvin: T₁ = 25 + 273 = 298 K, T₂ = 100 + 273 = 373 K Step 2: V₂ = V₁T₂/T₁ = (1.5)(373)/298 = 1.88 L Answer: 1.88 L

What is Gay-Lussac's Law and when is it applied?

Gay-Lussac's Law: At constant volume, pressure and temperature are directly proportional. Formula: P₁/T₁ = P₂/T₂. Applied when container volume cannot change (rigid container). Temperature must be in Kelvin.

Write the Combined Gas Law equation and explain when to use it.

Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂ Use when pressure, volume, AND temperature all change. Eliminate variables that remain constant. Combines Boyle's, Charles's, and Gay-Lussac's laws into one equation.

A gas at 2.0 atm, 3.0 L, 300 K changes to 1.0 atm, 400 K. Find final volume.

Using Combined Gas Law: P₁V₁/T₁ = P₂V₂/T₂ Given: P₁=2.0 atm, V₁=3.0 L, T₁=300 K, P₂=1.0 atm, T₂=400 K Step 1: V₂ = P₁V₁T₂/(P₂T₁) Step 2: V₂ = (2.0)(3.0)(400)/((1.0)(300)) = 8.0 L Answer: 8.0 L

State the Ideal Gas Law equation and define each variable.

Ideal Gas Law: PV = nRT P = pressure (atm) V = volume (L) n = number of moles (mol) R = gas constant = 0.0821 L·atm/(mol·K) T = temperature (K)

Calculate pressure of 2.0 mol gas in 5.0 L container at 300 K.

Using PV = nRT Given: n = 2.0 mol, V = 5.0 L, T = 300 K, R = 0.0821 Step 1: P = nRT/V Step 2: P = (2.0)(0.0821)(300)/5.0 Step 3: P = 49.26/5.0 = 9.85 atm Answer: 9.85 atm

What are Standard Temperature and Pressure (STP) conditions?

STP Conditions: - Standard Temperature: 0°C = 273.15 K - Standard Pressure: 1 atm = 760 torr = 760 mmHg - At STP: 1 mole of any gas occupies 22.4 L (molar volume)

How many moles of gas are in 44.8 L at STP?

At STP, 1 mole = 22.4 L (molar volume) Given: Volume = 44.8 L Step 1: moles = Volume/Molar volume Step 2: moles = 44.8 L / 22.4 L/mol = 2.0 mol Answer: 2.0 moles

Find the volume of 0.5 mol CO₂ at STP.

At STP: 1 mole = 22.4 L Given: n = 0.5 mol CO₂ Step 1: Volume = moles × molar volume Step 2: Volume = 0.5 mol × 22.4 L/mol = 11.2 L Answer: 11.2 L

What is the difference between real gases and ideal gases?

Ideal Gas: Hypothetical gas with no intermolecular forces, particles have no volume. Follows PV = nRT perfectly. Real Gas: Actual gases with weak intermolecular forces and particle volume. Deviates from ideal behavior at high pressure/low temperature.

Under what conditions do real gases behave most like ideal gases?

Real gases behave most like ideal gases under: 1. High temperature (particles move faster, overcome attractions) 2. Low pressure (particles far apart, minimal interactions) 3. Low density conditions Example: Most gases at room temperature and 1 atm pressure.

Calculate the density of nitrogen gas (N₂) at STP. (Molar mass N₂ = 28 g/mol)

At STP: 1 mol = 22.4 L Given: Molar mass N₂ = 28 g/mol Step 1: Density = mass/volume = molar mass/molar volume Step 2: Density = 28 g/mol ÷ 22.4 L/mol = 1.25 g/L Answer: 1.25 g/L

What is Avogadro's Law and its significance?

Avogadro's Law: At constant temperature and pressure, equal volumes of gases contain equal numbers of particles (molecules). V ∝ n (volume proportional to moles). Explains why 1 mole of any gas = 22.4 L at STP.

A container has 2 moles of gas at certain conditions. If moles increase to 6, what happens to volume?

Using Avogadro's Law: V ∝ n (at constant T, P) V₁/n₁ = V₂/n₂ Given: n₁ = 2 mol, n₂ = 6 mol Step 1: V₂/V₁ = n₂/n₁ = 6/2 = 3 Answer: Volume increases by factor of 3 (triples)

What is thermochemistry and why is it important?

Thermochemistry: Study of heat changes accompanying chemical reactions and physical changes. Important because: 1. Predicts if reactions release/absorb energy 2. Determines reaction spontaneity 3. Applications in energy production, metabolism 4. Understanding bond formation/breaking

Define enthalpy and explain its relationship to heat in chemical reactions.

Enthalpy (H): Total heat content of a system at constant pressure. ΔH = heat change in reaction. - ΔH negative (exothermic): Heat released, products more stable - ΔH positive (endothermic): Heat absorbed, energy required Measured in kJ/mol or cal/mol.

What happens to temperature when gases expand rapidly (adiabatic expansion)?

During rapid adiabatic expansion: 1. No heat exchange with surroundings 2. Gas does work against external pressure 3. Internal energy decreases 4. Temperature drops significantly Example: Spray can feels cold, air conditioning systems