Chemical Reactions and Stoichiometry
Master chemical reactions and stoichiometry — the mathematical heart of chemistry — with this comprehensive flashcard deck. Stoichiometry allows chemists to predict exactly how much of each substance is needed or produced in a reaction, making it essential for every branch of chemistry, from laboratory work to industrial manufacturing. This deck covers the five main types of chemical reactions, how to balance chemical equations, mole calculations, molar mass, limiting and excess reagents, theoretical and percent yield, concentration calculations, and gas stoichiometry. Essential for AP Chemistry, GCSE, A-Level, and university general chemistry.
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Question
What are the 5 main types of chemical reactions?
Answer
1. Synthesis: A + B → AB. 2. Decomposition: AB → A + B. 3. Single displacement: A + BC → AC + B. 4. Double displacement: AB + CD → AD + CB. 5. Combustion: Fuel + O₂ → CO₂ + H₂O.
Question
What is a synthesis (combination) reaction?
Answer
Two or more substances combine to form a single product. Example: 2H₂ + O₂ → 2H₂O. 2Na + Cl₂ → 2NaCl.
Question
What is a decomposition reaction?
Answer
A single compound breaks down into two or more simpler substances. Example: 2H₂O₂ → 2H₂O + O₂. Often requires heat, light, or electricity.
Question
What is a single displacement reaction?
Answer
A more reactive element displaces a less reactive element from a compound. Example: Zn + CuSO₄ → ZnSO₄ + Cu. Determined by the activity series.
Question
What is a double displacement (metathesis) reaction?
Answer
Ions of two compounds exchange partners. Example: AgNO₃ + NaCl → AgCl↓ + NaNO₃. Often forms a precipitate, gas, or water.
Question
What is a combustion reaction?
Answer
A substance (usually hydrocarbon) reacts rapidly with oxygen, releasing heat and light. Complete combustion: Fuel + O₂ → CO₂ + H₂O. Incomplete combustion produces CO and soot (C).
Question
What is the law of conservation of mass?
Answer
Matter cannot be created or destroyed in a chemical reaction. The total mass of reactants = total mass of products. This is why we balance equations.
Question
How do you balance a chemical equation?
Answer
Adjust coefficients (numbers in front of formulas) so the number of each type of atom is equal on both sides. NEVER change subscripts in formulas. Example: H₂ + O₂ → H₂O becomes 2H₂ + O₂ → 2H₂O.
Question
What is molar mass?
Answer
The mass in grams of one mole of a substance. Equal to the sum of atomic masses of all atoms in the formula. Example: H₂O = 2(1) + 16 = 18 g/mol.
Question
What is the mole formula triangle?
Answer
Moles = Mass (g) ÷ Molar Mass (g/mol). Rearranged: Mass = Moles × Molar Mass. Molar Mass = Mass ÷ Moles.
Question
What is stoichiometry?
Answer
The calculation of quantities (moles, mass, volume) of reactants and products in a chemical reaction, based on the balanced equation's molar ratios.
Question
How do you use molar ratios in stoichiometry?
Answer
The coefficients in a balanced equation give the mole ratio. Example: N₂ + 3H₂ → 2NH₃. If 1 mol N₂ reacts, it uses 3 mol H₂ and produces 2 mol NH₃.
Question
What is a limiting reagent (reactant)?
Answer
The reactant that is completely consumed first and determines the maximum amount of product that can be formed. The other reactant is in excess.
Question
How do you find the limiting reagent?
Answer
1. Convert each reactant to moles. 2. Divide moles by each reactant's coefficient. 3. The smallest result is the limiting reagent. Then use limiting reagent moles to calculate product.
Question
What is theoretical yield?
Answer
The maximum amount of product that could be produced if the reaction goes to completion with no losses. Calculated from stoichiometry using the limiting reagent.
Question
What is actual yield?
Answer
The amount of product actually obtained from an experiment. Always ≤ theoretical yield due to incomplete reactions, losses during collection, and side reactions.
Question
What is the percent yield formula?
Answer
% Yield = (Actual Yield ÷ Theoretical Yield) × 100%. A 100% yield is ideal but rarely achieved. A yield > 70% is generally considered good in organic chemistry.
Question
What is molarity (M) and its formula?
Answer
Molarity = concentration of a solution in moles per litre (mol/L). Formula: M = moles of solute ÷ volume of solution (L). Example: 2 mol NaCl in 0.5 L = 4 M NaCl.
Question
What is dilution and its formula?
Answer
Adding solvent to decrease a solution's concentration. Formula: M₁V₁ = M₂V₂ (moles before = moles after dilution). Example: Diluting 1 L of 6M HCl to 3 L gives 2 M HCl.
Question
What is the ideal gas law?
Answer
PV = nRT. P = pressure (atm), V = volume (L), n = moles, R = 0.0821 L·atm/mol·K, T = temperature (Kelvin). Describes behavior of an ideal gas.
Question
What is STP (Standard Temperature and Pressure)?
Answer
Temperature = 273 K (0°C) and Pressure = 1 atm. At STP, one mole of any ideal gas occupies 22.4 L (molar volume).
Question
What is an exothermic reaction?
Answer
A reaction that releases energy (heat) to the surroundings. ΔH is negative. The products have lower energy than the reactants. Example: combustion, neutralization reactions.
Question
What is an endothermic reaction?
Answer
A reaction that absorbs energy (heat) from the surroundings. ΔH is positive. Products have higher energy than reactants. Example: photosynthesis, dissolving ammonium nitrate in water.
Question
What is a precipitation reaction?
Answer
A double displacement reaction that forms an insoluble solid (precipitate) when two aqueous solutions are mixed. Example: Pb(NO₃)₂ + 2KI → PbI₂↓ (yellow precipitate) + 2KNO₃.
Question
What is an oxidation-reduction (redox) reaction?
Answer
A reaction involving the transfer of electrons. Oxidation = loss of electrons (OIL). Reduction = gain of electrons (RIG). OIL RIG — the substance oxidized is the reducing agent; reduced = oxidizing agent.