Topic 1: Stoichiometric Relationships Flashcards
Element
A substance that cannot be decomposed into simpler substances by chemical changes. It can exist as single atoms or molecules.
Compound
A substance made up of two or more elements, chemically combined.
Mixtures
Combinations of two or more pure substances in which each substance retains its own composition and properties. They do not have to be in the same state.
Homogenous Mixture
A homogenous mixture is made up of substances in the same phase. It appears uniform throughout.
Heterogenous Mixture
A heterogenous mixture is made up of substances in different phases. Visually distinctive components.
Solute
The substance being dissolved.
Solvent
The substance in which the solute dissolves.
The Kinetic Theory of Matter
The average kinetic energy of the particles is directly related to the temperature of the substance. (In simpler terminology, when we increase the temperature, we increase the kinetic energy of the substance.)
Give the definition of a State Change and explain why the temperature does not increase during this stage.
During a state change the energy added is used to break the intermolecular forces between the particles to cause the substance to change state, not to raise the kinetic energy, so the temperature remains constant.
Evaporation
The change of liquid to a gas. Evaporation occurs at the surface and takes place at temperatures below the boiling point i.e puddles on the street.
Boiling
Boiling occurs at a specific temperature (when the vapour pressure is greater than or equal to the atmospheric, external, pressure). It is characterized by bubbles, particles leaving the body of liquid.
Liquid
- Variable shape, fixed volume- Particles more spaced apart.- Weaker inter-particle forces, particles can slide over each other.
Solid
- Fixed shape and volume.- Closely packed particles.- Strong inter-particles forces, particles vibrate in lattice structure.
Gas
- Variable shape and volume.- Inter-particle forces are negligible, particles move freely. - Particles are spread out.
Define a mol
Amount of a substance that contains the same amount of atoms, molecules or particles in 12 grams of Carbon-12.
Relative Atomic Mass formula
relative atomic mass (Ar) = weighted average of one atom of the element/one twelfth mass of one atom of carbon-12
Define the relative atomic mass
The relative atomic mass (Ar) of an element is the weighted average of the masses of its isotopes relative to 1/12 of the mass of a carbon-12 atom.
Define the relative molecular mass
The relative molecular mass (Mr) of a substance is the weighted average of the masses of the molecules relative to the 1/12 of the mass of a carbon-12 atom.
Molecular Formula
The total number of atoms of each type in a molecule.
Empirical Formula
The lowest whole number ratio of atoms in a molecule.
Theoretical Yield
The maximum amount of product obtainable, assuming 100% of the limiting reactant is converted to product. Usually expressed in grams or moles.
Why may the experimental yield be different to the theoretical yield?
Reasons for low yield:- Loss during transfer. - Equilibrium/reaction did not go to completion. - Side reactions.Reasons for high yield:- Insufficient drying- Oxidation (gain of oxygen)- Side reactions
Molar concentration
Moles of solute per decimetre of solution. mol dm⁻³
Gases - Avogadro’s Law
Equal volumes of all gases, when measured at the same temperature and pressure, contain an equal number of particles.
Kinetic Molecular Theory
1) Particles are in constant motion2) That motion depends upon the absolute temperature measured in Kelvin
STP for gases
Standard Temperature and Pressure0°C = 273K1atm = 100kPa = 100,000Pa
Under STP 1 mol of gas occupies..?
22.7dm³ (This is called the molar gas volume Vm). Contains 6.02x10²³ molecules.
How do you write a net ionic equation?
Write balanced molecular equationWrite the state symbols (s, l, g, aq) for each substanceSplit strong electrolytes into ions (the complete ionic equation)Cross out the spectator ions that appear on both sides of the complete equationWrite the remaining substance as the net ionic equation
What are common spectator ions?
NO₃²⁻, Na⁺, K⁺
