Chapter 2: Atoms, Molecules And Stoichiometry Flashcards
(17 cards)
Define the mole in terms of the Avogadro constant.
A mole is the amount of substance containing the same number of particles as there are in 12 g of carbon-12, which is Avogadro’s constant (L) = 6.022 × 10²³ mol⁻¹.
Avogadro’s constant is fundamental in chemistry for converting between moles and number of particles.
How do you calculate the number of particles using the Avogadro constant?
Number of particles = moles × Avogadro constant.
This formula is essential for determining the total number of atoms, molecules, or ions in a sample.
What is the formula to calculate moles from the number of particles?
Moles = number of particles ÷ Avogadro constant.
This formula allows conversion from a specific number of particles back to moles.
How do you calculate the relative atomic mass of an element given the relative abundances of its isotopes?
Ar = (isotope₁ × %abundance + isotope₂ × %abundance + …) / 100.
This formula is used to find the weighted average of isotopic masses based on their natural abundances.
Define empirical formula.
The simplest whole-number ratio of atoms in a compound.
Empirical formulas provide a basic understanding of the composition of compounds.
Define molecular formula.
The actual number of atoms of each element in a molecule.
Molecular formulas give precise information about the quantity of each atom in a compound.
What are the steps to deduce empirical and molecular formulae from combustion data or composition by mass?
- Convert masses to moles.
- Divide by the smallest number of moles.
- For molecular formula: molecular mass ÷ empirical mass gives the multiple.
These steps are crucial for determining the formulas of unknown substances based on experimental data.
How do you deduce the formulae of ionic compounds?
Balance charges between ions to get a neutral compound.
This process ensures that the total positive charge equals the total negative charge in the compound.
What is the principle behind writing and constructing balanced chemical equations?
Use conservation of mass to balance equations.
Conservation of mass states that matter cannot be created or destroyed in a chemical reaction.
What should be included in ionic equations?
Show only species involved in the chemical change (omit spectator ions).
This focuses on the actual reactants and products that undergo a change during the reaction.
How do you apply stoichiometric relationships in calculations?
Apply mole ratios from the balanced equation to determine unknown masses, volumes, or numbers of moles.
Stoichiometry is fundamental in predicting the outcomes of chemical reactions.
How do you calculate the amount of substance from mass or volume?
Use the appropriate formulas based on the context of the problem.
This involves using molar mass for mass calculations and concentration for volume calculations.
What is the formula to calculate concentration?
c = n / V (mol dm⁻³).
This formula is used to find the concentration of a solute in a solution.
What is the ideal gas equation?
pV = nRT (p in Pa, V in m³, R = 8.31 J mol⁻¹ K⁻¹, T in K).
This equation relates the pressure, volume, temperature, and amount of gas in a sample.
What is a limiting reagent?
The reactant that runs out first and limits the amount of product formed.
Identifying the limiting reagent is crucial for calculating theoretical yields in reactions.
How do you calculate percentage yield?
% yield = (actual yield ÷ theoretical yield) × 100.
This calculation helps evaluate the efficiency of a chemical reaction.
What is the formula for calculating atom economy?
Atom economy = (molar mass of desired product ÷ total molar mass of products) × 100.
Higher atom economy indicates a more efficient use of resources in chemical reactions.
