Chemistry Definitions Flashcards
Define one mole.
The amount of substance having the same number of particles as there are atoms in 12g carbon-12.
Definition of Avagadro’s Number.
The number of particles in one mole.
Define Molecular Mass.
Sum of all the atomic masses of all the atoms in a molecule of a substance.
Define Relative Atomic Mass.
The ratio of the average mass per atom of an element to 1/12 of the mass of a carbon-12 atom.
Define Relative Molecular/Formula Mass.
The sum of the relative atomic masses of the atoms in the molecule.
Define Molar Mass.
The mass of one mole of a substance measured in g.mol-1.
What is concentration?
The amount of solute per litre of solution.
What is percentage composition?
It expresses the mass of each element in a compound as a percentage of the total mass of the compound.
Define Molecular Formula.
The actual ratio of atoms in a molecule or compound.
Volume of gases at STP.
One mole of any gas has a volume of 22,4dm3 at 273 K (0 degrees) and 101,3 kPa (1 atmosphere).
What is Avagadro’s Law?
Equal volume of all gases, measured at the same temperature and pressure, contain the same number of molecules.
Define the term standard solution.
Any solution that has a precise, known concentration.
What is a limiting reagents?
The reactant that is used up first during a reaction. It determines the amount of product that forms.
Define what an excess reactant is.
It is the reactant of which some remains at the end of the reaction.
Define enthalpy.
The total amount of chemical potential energy in a chemical system.
What is an endothermic reaction?
A reaction that absorbs energy.
Define what an exothermic reaction is.
A reaction that releases energy.
What is bond energy?
The energy absorbed when bonds break, or released when new bonds form.
Define collision theory.
It states that for a reaction to occur between atoms, ions or molecules, they must collide.
How must particles collide to make collision effective?
- with sufficient energy
* with correct orientation
Define what activation energy is.
The minimum energy needed for a faction to take place.
What is the activated complex?
The unstable transition state from reactants to products.
What is a catalyst?
A substance that changes/increases the rate of a reaction without itself undergoing a permanent change or being used up.
Define what an Arrhenius Acid is.
An acid is a substance that produces hydrogen ions (H+) / hydrogen ions (H30+) when it dissolves in water.
What is an Arrhenius Base?
A base is a substance that produces hydrogen ions (OH-) when it dissolves in water.
What are the limits to the Arrhenius Theory?
- It doesn’t explain reactions with solvents which aren’t water.
- It doesn’t explain bases such as NH3 that still produce (OH-) but contain no oxygen.
Brønsted-Lowry Acid:
An acid is a proton (H+ ion) donor.
Brønsted-Lowry Base:
A base is a proton (H+ ion) acceptor.
What is a monoprotic acid?
An acid which can only donate ONE proton.
What is a Polyprotic Acid?
An Acid which can donate MORE than one proton.
What is a conjugate acid-base pair?
- When an acid donates a proton it becomes a conjugate base.
* When a base accepts a proton it becomes a conjugate acid.
Define the term ampholyte.
It is an amphiprotic substance. It is a substance that can act as either a base or an acid.
What is an acid-base indicator?
It is a weak acid or base which changes colour as the H+ ion concentration or the (OH-) ion concentration in a solution changes.
Define the term acid-base titration. (Neutralisation)
The reaction between an acid and a metal hydroxide (base).
What is oxidation and reduction?
- Oxidation: the loss of electrons.
* Reduction: the gain of electrons.
Define reducing agent.
A substance that is oxidised / that loses electrons / whose oxidation number increases.
What is a oxidising agent?
A substance that is reduced / that gains electrons / whose oxidation number decreases.
What is an oxidation number?
The oxidation number of an element is a number assigned to each element in a compound to keep track of the movement of electrons during a reaction.
What is an electrolyte?
A solution which is able to conduct an electric current.
What is the function of a salt bridge?
To keep the electrolyte solutions neutral.
