Structure 1.1 Flashcards
What are elements?
Primary constituents of matter, they cannot be chemically broken down into simpler substances
Chemical Element
A neutral substance that cannot be chemically broken down into simpler substances. It consists of only atoms that contain the same number of protons.
Compound
A pure substance occurring when two or more chemical elements are chemically bonded together. It has different properties from its component elements.
Solids
Occupy a fixed space and volume. Particles held closely together in a lattice.
Liquids
Fixed volumer that takes the shape of its container. Particles are close together but move with random motion.
Gases
Completely fill their container particles are widely spaced and move with rapid random motion.
Heat
A measure of the total amount of energy in a given amount of substance. Depends on the amount of substance present. Measured in Joules (J)
Temperature
The measure of the average kinetic energy or ‘hotness’ of a substance. Independent of the amount of substance present. Measured in Kelvin.
What happens at 0K?
All motion has stopped. Absolute zero
Litre to Meter conversions
mL=cm^3
L=dm^3
When do liquids boil?
When their vapour pressure equals atmospheric pressure. Lowering/raising will lower/raise the boiling point.
Melting
Changing from a solid to a liquid
Freezing
Changing from a liquid to a solid
Vaporisation
Changing from a liquid to a gas
Evaporation
Changing from a liquid to a gas below the boiling point
Boiling
Changing from a liquid to a gas when the vapour pressure equals the external pressure
Condensation
Changing from a gas to a liquid
Sublimation
Changing from a solid to a gas without going through a liquid state
Deposition
Changing from a gas to a solid without going through the liquid state
What is the arrangement of particles in the solid state?
In the solid state, particles are closely held together in a fixed position within a lattice structure. They can vibrate about a fixed point.
What happens to solid particles as heat is supplied?
As heat is supplied, the vibration of particles intensifies. Eventually, they gain enough energy to break the lattice structure, and the particles become free to move, entering the liquid state.
What is the liquid state in terms of particle behavior?
In the liquid state, particles are free to move, but there are still attractive forces between them. The particles have more energy than in the solid state but are not completely free.
How do particles behave as more heat is added to a liquid?
As more heat is added, particles move faster and gain kinetic energy. Eventually, they have enough energy to overcome attractive forces and escape as vapor.
What is the boiling point, and how does it relate to external pressure?
The boiling point is when the vapor pressure equals the external pressure. The boiling point depends on the external pressure. For example, at 100 kPa, water boils at 373 K (100°C).
Reason for the plateau in cooling curves
The temperature remains constant as an equilibrium is established between the heat given out (due to the formation of attractive forces between particles) and the heat being lost to the environment.
Pure substance
Either an element or compound with a definite and constant composition.
Mixture
A physical combination of pure substances. They have no definite or constant composition. It can be separated into its pure substances by physical means. May be heterogenous or homogenous
Homogenous
All components in the same phase (eg. components are all liquids)
Heterogenous
Components are in different phases
Is it hetero or homogenous if there is a physical boundary between the two phases?
Heterogenous
solute
the solid substance being dissolved
solvent
the liquid that dissolves the solute
solution
when a solute dissolves in a solvent (final mixture)
soluble
a substance that can dissolve in a solvent
insoluble
a substance that cannot dissolve in a solvent
miscible
two liquids that can dissolve into each other
immiscible
two liquids that cannot dissolve into each other
Are all ionic compounds soluble in water?
No, while most are strong electrolytes that fully dissociate, some are insoluble. These compounds still exchange ions with the solution, creating a heterogeneous equilibrium that favors the solid lattice.
Precipitation reaction
When two soluble ionic compounds are mixed and an insoluble compound is formed
Methods of separating mixtures
Filtration, Solvation and evaporation, recrystallisation, distillation, reflux, chromatography.
Filtration
To separate insoluble solid particles (residue) from a liquid (filtrate).
Solvation and evaporation
Used when one component of a mixture of solids is soluble. Mixture is warmed with the solvent, filtered to remove insoluble particles. The filtrate has the solvent removed by evaporation leaving the soluble particles.
Recrystallisation
Recrystallization is a process where an impure solid is dissolved in a suitable solvent by heating. As the solution cools slowly, pure crystals form, which can be washed to remove lingering solvent and then dried.
Distillation
Used to seperate a volatile liquid from a less volatile liquid or dissolved components. Useful with liquids of different boiling points. Fractional distillation is used for liquids of very similar boiling points.
Reflux
Used to heat volatile mixtures without losing any volatile components. Heating is used to increase rate of rxn
Chromatography
Chromatography separates components in a mixture by placing a spot of the mixture on the paper. As the solvent (eluent) rises, components partition between the solvent and the paper at different rates, separating them. A developer can be used for colorless components.
Formula for the retardation factor
distance travelled by the solvent from the original spot.
