Unit 1 - Chemical Changes & Structure Flashcards
What is collision theory?
Collision theory is the conditions required for particles to react and make more ‘successful’ collisions
A successful collision means a particle will…
3 things
Collide frequently
Collide in correct alignment
Have enough energy to overcome activation energy
What is activation energy
The minimum kinetic energy needed by colliding particles in order for a chemical reaction to take place
How fast would the rate of a reaction be if it had a high Ea
Slow
How fast would the rate of a reaction be if it had a low Ea
Fast
How does a catalyst speed up a chemical reaction
A catalyst speeds up a chemical reaction by lowering Ea. It does not get involved or used up.
What does a potential energy diagram tell
If a reaction is endothermic If a reaction is exothermic Where the activated complex is Ea Enthalpy change
How do you tell if a reaction is endothermic from a potential energy diagram
It ends with more energy showing that it had gained energy
How do you know of a reaction is exothermic from a potential energy diagram
It ends with less energy showing that or has released energy
How do you calculate enthalpy change
Product-reactants
How do you calculate activation energy
Highest point-reactant energy
What is activated complex
The activated complex is the arrangement of atoms produced when old and new bonds are breaking and forming. It is a highly unstable arrangement of atoms that exists for a fraction of a second
What is the effect of concentration on rate of reaction
The more reactant particles present the more successful collisions so faster rate
These reacting particles have enough kinetic energy to overcome activation energy
What is the effect of temperature on taste of reaction
As temperature increases reaction rate increases
This is because temperature increases makes particles move faster, they have more successful collisions and have enough energy to overcome Ea
What is temperature
Temperature is a measure of the average kinetic energy of particles in a substance
Which reaction rate is higher, graph 1 or graph 2? Why?
The rate of reaction in graph2 is higher than in graph 1 because there is less energy required to overcome activation energy increasing the number of successful collisions
What is the only thing that can change the position of Ea
A catalyst
Why are atoms in metallic bonding tightly packed
Because the delocalised electrons are moving from atom to atom
This strong electrostatic attraction between the positive nucleus and the delocalised electrons creates a strong bond which acts in all directions around each atom
What is the relationship between boiling point and alkali metals
As the atomic number increases the boiling point decreases
Because:
Down group 1 energy levels increases
Positive nucleus has a weaker hold on outer electrons
Less energy required to break the bond
Boiling point value decreases
What is the relationship between period 4 and the boiling point
As atomic number increases the boiling point increases
Because:
Across period 4 electrons don’t increase but number of electrons in outer shell does
Positive nucleus has a stronger hold on the outer electrons
More energy is required to break the bond
Boiling point value increases
What are the types of molecular forces
Intermolecular and intermolecular
What are intermolecular forces
Between molecule
these are weak
What are intermolecular forces
Within molecules
These are strong
What is a molecule
A small covalent compound
What are LdF’s
London dispersion forces are formed from electron wobble. This forms temporary dipoles. These are the weakest of all WdW forces.
Not much energy is required to break them
What is the relationship between boiling point and the noble gasses
As the atomic number increases the boiling point increases Because: Down the group there is more electrons More e- = more e- wobble More e-wobble = more temporary dipoles Stronger LdF’s = more energy to break
What is the relationship of atomic size as it goes down a group
As you go down a group the atomic size increases as there is an extra electron shell
What is the relationship of atomic size as you go along a period
There is a positive charge on the nucleus. It had a pulling effect on the outer electron level bringing the levels closer so atomic size decreases
What is ionisation
This is the energy required to remove an electron from the atom of an element in a mole of free atoms
How many times can sodium be ionised
11 times
Because it has 11 e-
What is the relationship between halogen size and melting point
As the halogen size increases the melting point increases
Because:
The bigger the halogen the more electron levels which means stronger London Forces. This means more energy is needed to break those bonds
What is the relationship between increasing the number of atoms of hydrocarbons and melting point
The atomic size remains the same as the hydrocarbons only contain hydrogen and carbon
There are more atoms which means more e- wobble
This means stronger LdF’s
Which means more energy is needed to break attraction
What is electronegativity
Electronegativity is the measure of attraction of covalently bonded electrons between atoms
