Unit 1 Flashcards
What must happen before a reaction can take place?
The particles must collide
4 Ways ti increase rate of reaction
Decrease particle size/increase surface area.
Increase concentration
Increase temp
Add a catalyst
How does increasing the surface area work
The larger the surface area, the more particles available to react therefore more collisions and a higher rate of successful reactions
How does incrreasing conc work
The higher the concentration, the more particles, this means a higher chance of collisions and more successful reactions
How does increasing temp work
More particles are moving faster so there are more collisions and more particles with energy greater than the activation energy
Name the two things needed for a successful reaction
Sufficient energy and correct geometry
What is an activated complex
As a reaction proceeds from reactants to products, an intermediate stage is reached at the top of the activation barrier at which a highly energetic species called an activated complex is formed
What is activation energy
Activation energy is the minimum kinetic energy required by colliding molecules for a reaction to occur
Difference between Endo/Exothermic
Exothermic reactions give out energy, therefore the products have less energy than the reactants
Endothermic reactions take in energy from their surroundings, therefore the products have more energy that the reactants
How do you find the enthalpy change
The difference in energy between reactants and products
Why is it essential that chemists can predict the quantity of heat taken in or given out in an industrial process
Runaway reactions such as those causing the disasters in Bhopal and Seveso occur when the rate at which a chemical reaction releases energy exceeds the capabilities of the plant to remove heat. Also, Endothermic reactions require heating which is costly
What is temperature
Temperature is a measure of the average kinetic energy of the particles in a chemical
How to catalysts work
They lower the activation energy for a reaction, making it easier for the activated complex to form
Reactivity if Groups
Group 1 - Reactivity increases downwards
Group 7- Reactivity decreases downwards
Group 0 - Unreactive
What are periods and groups
Along the way - Period
Down the way - Group
Why do certain elements have similar properties
Same number of outer electrons
How are covalent bonds formed
Shared pair of electrons
Behaviour of outer electrons in metallic bonding
Electrons are delocalised
Difference between covalent network and molecular
Molecular elements or compounds have a definiteb number of atoms binded together. Network ____ have a vast but indefinite number of atoms bonded together
Explain Covalent radius
It’s a measure of the size of an atom. It decreases along a period, and increases down a group
How does nuclear charge/occupied shells affect Covalent radius
As you go across a period the nuclear charge become more positive so the shells of electrons are more strongly attracted and pulled in tighter. As you do down a group there is an increasing number of occupied shells. This increases the covalent radius
What is first, secind and third ionisation energies
The first ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in its gaseous state. The second ionisation energy (and subsequent) refer to the energies required to remove further moles of electrons
Use atomic size and screening effect to explain the change in ionisation energies down a group
As you go down, the atoms are bigger as there is another shell of electrons. The outer electrons are further from the positive pull of the nucleus and are also shielded from its full effect by the inner electrons. This makes it easier to remove the outer electron and so there is a lower ionisation energy.
Use atomic size and nuclear charge to explain the change in ionisation energy across a period.
As you go across, the positive charge of the nucleus increases which pulls the electrons in together and makes the atom smaller. The outer electrons are closer to the nucleus so more strongly attracted this makes the removal of an electron more diffuse the ionisation energy increases
