Chemical Changes and Structure Flashcards
Describe how the progress of a chemical reaction can be measured
Measure how fast the product is produced (normally the volume of gas produced)
Measure how fast the reactant is used up (normally the weight of a reaction)
Describe ways of increasing the rate of a reaction
To increase the rate, the number of collisions in a reaction need to be increased.
Increase the temperature - this gives the particles more energy, when they are moving faster they are more likely to collide with each other
Increase the concentration - this increases the number of particles, the more particles the more collisions
Decreasing the particle size - this increases the surface area so therefore more ‘space’ for collisions
Adding a catalyst
Describe the term catalyst
A substance that can speed up the rate of a reaction without being used up itself (it can be recovered unchanged at the end of a reaction).
An example is iron in the Haber Process or platinum in a catalytic convertor.
State the definition of an isotope
An isotope is two or more forms of the same element which have the same number of protons but different number of neutrons OR same atomic number but different mass number.
(Both definitions are accepted answers).
State the definition of an atom’s relative atomic mass
The relative atomic mass (RAM) is the average mass of all the atoms of an element in a given sample.
The RAM of each element is stated on P7 of the data booklet.
Describe a covalent bond
A covalent bond is between 2 or more non-metal atoms.
It is the attraction a positive nuclei has for a shared pair of electrons.
It is stable as opposite charges attract. The negative electrons are attracted to the positive nucleus of the other atom.
State and predict the different shapes of covalent molecules
Covalent molecules come in 4 shapes.
The shape of a molecule can be predicted by the chemical formula of a molecule as it is dependant on the number of bonds and the orientation of them.
Linear-2
Angular-3
Trigonal Pyramidal-4
Tetrahedral-5
Ions
Ions are atoms which have lost or gained electrons.
They lose/gain atoms to obtain a full outer shell of electrons (usually 8).
Metal atoms LOSE electrons to become POSITIVELY charged.
Non-metals GAIN electrons to become NEGATIVELY charged.
Describe an ionic bond and their structure
An ionic bond is between metal and non-metal atoms. It is the electrostatic attraction between positive and negative ions.
They are formed by metal atoms ‘donating’ electrons to non-metal atoms. This forms positive and negative ions which are then attracted to each other.
They are described as IONIC LATTICE structures - large structures of a repeating pattern of negative ions surrounded by positive ions and each positive ions surrounded by negative ions.
Explain the properties of an ionic compound
They have high melting and boiling points as they contain strong ionic bonds which must be broken in order to change state (and to break up lattice structure).
They cannot conduct as a solid - they have charged particles but they are not free to move.
They can conduct as a liquid or in solution as their charged particles (ions) are free to move towards oppositely charged electrodes.
They are soluble in water as they dissolve the lattice structure breaks up so the ions can move and be surrounded by water molecules.
Describe solute, solvent and solution
Solute - the solid that is dissolved in the solvent.
Solvent - a liquid that is able to dissolve a substance.
Solution - what is formed when a solute is dissolved in a solvent.
State the definition of the pH scale
A measure of how acidic or alkaline a substance is.
Anything with a pH below 7 is acidic, a pH above 7 is alkaline and a pH of 7 is neutral.
Write the equation for the dissociation of water
H2O(l) ⇋ H+(aq) + OH- (aq)
State the definition of a neutralisation reaction
A neutralisation reaction is when a base and an acid react together to form a neutral solution and salt.
(Bases are substances that react with acids - bases which dissolve in water are alkalis).
Explain what happens during a titration
A titration is an experimental method of determining the concentration of a solution.
A solution of known concentration is added to a set volume of the solution of unknown concentration until the reaction is neutralised.
The end point is normally determined by a colour change. The unknown concentration can then be calculated
