gas laws
According to Boyle’s Law, what happens to the volume of a gas if the pressure increases while temperature remains constant?
When gas particles are squeezed closer together, they collide more often, reducing volume.
State the First Law of Thermodynamics and explain what it means in simple terms
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transferred or transformed
What is the difference between a strong electrolyte, weak electrolyte, and nonelectrolyte? Give one example of each.
Strong electrolyte: completely dissociates into ions → conducts electricity well.
Example: NaCl(aq) → Na⁺ + Cl⁻
Weak electrolyte: partially ionizes → conducts weakly.
Example: HF(aq) ⇌ H⁺ + F⁻
Nonelectrolyte: does not form ions in solution → no conductivity.
Example: C₆H₁₂O₆ (glucose)
According to the Bronsted–Lowry definition, what is the difference between an acid and a base? Give one example of each.
Acid: proton (H⁺) donor → Example: HCl → H⁺ + Cl⁻
Base: proton (H⁺) acceptor → Example: NH₃ + H⁺ → NH₄⁺
What does molarity (M) measure, and how is it defined?
Molarity (M) measures the concentration of a solute in a solution.
M= n/L
Explain why a balloon expands when heated and shrinks when cooled, assuming pressure is constant
When temperature increases, gas molecules move faster and spread apart → balloon expands.
When cooled, motion slows → volume decreases
What is the difference between an endothermic and an exothermic process? Give one example of each.
Endothermic: The system absorbs heat from surroundings (q > 0).
Example: ice melting, water boiling.
Exothermic: The system releases heat to surroundings (q < 0).
Example: combustion of methane, freezing of water
According to the solubility rules, which of the following compounds are soluble in water and which are insoluble?
a) NaNO₃
b) BaSO₄
c) AgCl
d) K₂CO₃
NaNO₃ → soluble (all nitrates are soluble)
BaSO₄ → insoluble (most sulfates are soluble except Ba²⁺, Pb²⁺, Ca²⁺)
AgCl → insoluble (chlorides are soluble except Ag⁺, Pb²⁺, Hg₂²⁺)
K₂CO₃ → soluble (all K⁺ and Na⁺ salts are soluble)
What makes an acid or base strong or weak in aqueous solution?
Strong acids/bases ionize completely → produce many ions.
Example: HCl, NaOH
Weak acids/bases partially ionize → few ions.
Example: HF, NH₃
If the same amount of solute is dissolved in a larger volume of water, what happens to the molarity?
The molarity decreases because concentration depends on both moles and volume.
→ Increasing volume spreads the solute out more, so there are fewer moles per liter.
A sealed aerosol can warns “Do not heat.” Using Gay-Lussac’s Law, explain why.
Heating increases molecular speed → more collisions → higher pressure.
If overheated, pressure may exceed the can’s limit → can explodes.
In thermodynamics, what is meant by “work done by a system” and “work done on a system”?
Work done by a system: when the gas expands, it pushes the surroundings — energy leaves the system (w < 0).
Work done on a system: when the gas is compressed, surroundings push on it — energy enters the system (w > 0).
When solutions of Na₂SO₄(aq) and BaCl₂(aq) are mixed, will a precipitate form? Explain using solubility rules and write the net ionic equation.
Prediction: BaSO₄ is insoluble → precipitate forms.
Net Ionic Equation:
Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
What happens during an acid–base neutralization reaction, and why is the resulting solution not always neutral?
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O
If the acid and base are equally strong, the solution is neutral (pH = 7).
If one is stronger or in excess, the solution can be acidic or basic after neutralization
Explain what happens during a dilution and why the equation M1V1=M2V2M_1V_1 = M_2V_2M1V1=M2V2 can be used.
During dilution, water is added to a solution — the number of moles of solute stays the same, but the volume increases.
M1V1=M2V2M_1V_1 = M_2V_2M1V1=M2V2
Because moles before = moles after.
➡️ Molarity decreases, but total solute doesn’t change.
In the combined gas law, describe what happens to the volume of a gas if both pressure and temperature decrease simultaneously
Lower pressure → tends to increase volume.
Lower temperature → tends to decrease volume.
➡️ The net effect depends on which change is greater. If temperature drop is more significant, gas volume decreases overall; if pressure drop dominates, volume increases
What is the difference between heat capacity (C) and specific heat (c), and how do they relate to how substances heat up or cool down?
Heat capacity (C): amount of heat needed to raise the temperature of an entire object by 1°C (depends on mass and material).
Specific heat (c): heat required to raise 1 gram of a substance by 1°C (intrinsic property).
Explain what happens when HCl(aq) is mixed with NaOH(aq) and why this reaction is not a precipitation reaction.
HCl and NaOH undergo a neutralization reaction, not a precipitation.
Reaction: H⁺(aq) + OH⁻(aq) → H₂O(l)
Determine the oxidation number of each element in the compound H₂SO₄ and explain the steps.
H = +1, S = +6, O = –2
Two solutions of NaCl are labeled 0.10 M and 1.0 M. How do these differ in terms of particle concentration and physical properties (like conductivity)?
1.0 M NaCl has 10× more ions (Na⁺, Cl⁻) per liter than 0.10 M.
It conducts electricity more strongly because more charged particles move through the solution.
➡️ Higher molarity = higher ion concentration = greater conductivity and reactivity
Why do real gases deviate from the ideal gas law (PV = nRT) at high pressures or low temperatures?
The Ideal Gas Law assumes:
Gas particles have no volume.
There are no intermolecular forces.
At high pressure → gas particles are close, their own volume matters.
At low temperature → attractive forces between molecules become significant.
➡️ Real gases condense or deviate because the ideal assumptions break down under these conditions.
When two objects at different temperatures are placed in contact, why does heat always flow from the hotter to the colder object, and what happens when they reach equilibrium?
Heat flows spontaneously from high temperature → low temperature because this direction increases the entropy (disorder) of the universe.
At thermal equilibrium, both objects reach the same temperature, and no net heat flow occurs.
Consider the following reactions. Identify which one forms a precipitate and which one does not, and explain why using solubility rules:
a) AgNO₃(aq) + NaCl(aq) → ?
b) NaNO₃(aq) + KCl(aq) → ?
a) AgNO₃ + NaCl → AgCl(s) + NaNO₃(aq)
AgCl is insoluble, so a white precipitate forms.
→ Chlorides are soluble except with Ag⁺, Pb²⁺, Hg₂²⁺.
b) NaNO₃ + KCl → no reaction
All products are soluble (nitrates and alkali metals are always soluble).
In the reaction Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s):
assign oxidation numbers to all species,
identify which element is oxidized and which is reduced,
and explain how you know.
Zn is the reducing agent (it donates electrons), and Cu²⁺ is the oxidizing agent (it accepts them).
Why is molarity a useful unit in chemistry? Give practical examples
Molarity links measurable quantities (volume + mass) to chemical ratios.
In chemistry labs, it lets you mix acids/bases precisely for neutralization.