Unit 1: Chemical Changes and Structure Flashcards
(20 cards)
What is collision theory?
Before a collision takes place, the particles must collide with each other and have the correct collision geometry.
What is an activated complex?
At the top of the activation barrier, a highly energetic species s formed.
What is the activation energy?
The minimum kinetic energy required by colliding molecules for a reaction to occur.
What is temperature?
The average kinetic energy of the particles in a substance.
What does a catalyst do?
It affects the activation energy by lowering it.
What is enthalpy?
A measure of the energy stored in a chemical (H).
What does an exothermic reaction do?
Gives out heat energy to the surrounding.
e.g combustion, displacement, neutralisation and respiration.
Enthalpy change is negative.
Products have less energy than reactants.
What does an endothermic reaction do?
Takes in heat from the surroundings.
e.g photosynthesis
Enthalpy change is positive.
Products have more energy than reactants.
What is a heterogeneous reaction?
The catalyst is in a different physical state from the reactants e.g solid catalysts such as metals speeding up the reaction of liquids or gases.
What is a homogeneous reaction?
The catalyst is in the same physical state as the reactants.
What is a catalyst?
A substance that speeds up the rate of reaction while remaining unchanged.
What is the bonding is metals?
The strength of metallic boding depends on the number of delocalised electrons per atom.
Increases along a period, decreases down a group.
Mp and Bp usually high.
What is the bonding in monatomic gases?
Nobles gases exist as single atoms with weak forces between them.
What is the bonding in covalent molecular?
Low Mp and Bp as only weak intermolecular forces between molecules need o be broken.
Exist as gases or liquids at room temperature
What is the bonding in covalent network?
High Mp and Bp- thousands.
Strong covalent bonds need to be broken.
Exist as solids.
How are the protons and electrons arranged in covalent, ionic and metallic bonds?
Covalent- Protons in nucleus, shared electrons.
Ionic- Protons in nucleus, lose or gain electrons.
Metallic- Protons in nucleus, delocalised electrons.
What is the covalent radius?
Half the distance between the nuclei of two covalently bonded atoms.As you go down a group there is another shell of electrons and the size of the atoms increase.
What is ionisation energy?
The first ionisation energy of an element is the energy required to remove one mole of electrons from one mole of atoms in the gaseous state.
The strength of metallic bonding increases across a period because…
…more outer electrons become delocalised.
The strength of metallic bonding decreases down a group because…
…you’re adding an extra energy level each time which creates more of a shield from the positive nucleus to the delocalised electrons.
