Unit 1 - Chemical Changes and Structure Flashcards
What is Collision theory?
The collision theory states that for a chemical reaction to occur particles must collide with a minimum of kinetic energy (called the activation energy) and the correct orientation of geometry
What is the activated complex?
The activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction. It is where the bonds between the reactants have not fully broken and the new bonds have not fully formed.
Using collision theory to explain the effect of particle size
Decreasing the particle size of a solid reactant increases the number of possible collisions (increasing the surface area). This increases the number of successful collisions and increases the reaction rate.
Using the collision theory to explain the effect of concentration
Increasing the concentration of a reactant increases the number of particles in a given volume, which means there are more successful collisions. This increases the reaction rate.
Using the collision explain the effect of pressure on a gaseous reactant
Increasing the pressure of a gaseous reactant increases the concentration of the gas (more particles are squashed into a smaller volume) so there are more successful collisions and the reaction rate increases
Using collision theory to explain whey a 10C rise in temperature doubles the rate
When the temperature rises by 10C, the rate of the reaction increases because the average kinetic energy of the colliding particles increases. This means that the more particle collide with the activation energy, resulting in more successful collisions.
What is a catalyst?
Catalysts increase the rate of a reaction by providing an alternative reaction pathway with a lower activation energy.
What is a homogenous catalyst?
Homogenous catalyst exist in the same state as the reactants
What is a heterogenous catalysts?
Heterogenous catalysts exist in a different state to the reactants
Name the three steps of the active site of a heterogenous catalyst
1) ADSORPTION
Molecules of one or both reactants form bonds with the catalyst. This weakens the bonds within the molecules
2) REACTION
The molecules react on the catalyst surface. The angle of collision is more likely to be favourable since one of the molecules is fixed
3) DESORPTION
The product molecules leave the catalyst and the vacant site can be occupied by another reactant molecule
Why is there an energy change when chemicals react?
The reactants and products have different energies
Explain an exothermic reaction
The products have less energy than that of the reactants therefore energy is lost to the surroundings in the form of heat e.g burning a fuel
Energy change -VE
Explain an endothermic reaction
The products have more energy than the reactants therefore energy is gained from the surroundings
Energy change +VE
What is the atomic radius?
The atomic radius of an element is half the distance between the nuclei of two bonded atoms of the element.
What is the pattern in atomic size going across a period?
As we move across a period the covalent atomic radius decreases (the atoms get smaller) because the nuclear charge increases, attracting the outer electrons more strongly, pulling them in closer; without any additional shielding.
