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C7 (Chemical change vs physical change, Collision theory, Reversible…
C7
Chemical change vs physical change
Chem change
Occur at molecular level when two or more molecules interact
Physical change
Relate to change in physical state of matter
Collision theory
Two conditions must be met for chem rxn to occur
1) Two (or more) particles must collide
2) Particles must have sufficient energy to react
Rate of reaction
1) Concentration
Higher conc = higher collision rate = higher rate of rxxn
Suggests that the higher concentration the more the particles
2) Pressure (Gas only)
High pressure = higher collision rate = Higher rate of rxn
3) Temp size
Higher temp = higher collision rate AND higher particular energy = Higher rate of rxn
4)
Particle size (solids only)
Smaller particle size = larger surface area (For collision) = higher rate of rxn
5) Catalyst
Does not get used in chem rxn but increases rate
Reversible reactions
Reacts from products and products react to form back reactants
At some point, rate of forward reaction will = rate of reverse reaction
Means concentration of products and reactions
This is called equilibrium
Position of equilibrium
Concentrations of reactants and particles in an equilibrium is called "position of equilibrium"
Shift to right suggest that more A and B get used up to make
Meaning equilibrium concentrations of A and B go down, but of C will increase
Shift to left suggest more c gets used up to make A and B,
so concentration of C decreases whilst A and B increases
Position of equilibrium always shifts in direction opposing change (in condition) imposed
depending on change in conditions, position of equilibrium can shift either left or right.
1) Concentation
Inc in product conc will shift equilibrium to left
dec in product conc will shift equilibrium to right
inc in reactant conc will shift equilibrium to right
dec in reactant conc will shift equilibrium to left
2) Temperature
Inc in temp will favor endothermic rxn
Dec temp will favor exothermic rxn
3) Pressure
Inc pressure will shift equilibrium towards side with lower number of particles
Dec pressure will shift equilibrium towards side with larger number of particles
4) Catalyst
Does not shift equilibrium at all. Increases rate of reaction only (of both forward and reverse rxn)
Redox
Reduction and oxidation can be demonstrated in two different ways
1) Oxxygen gain or loss
Oxidation is the gain of oxygen
Reduction is the loss of oxxygen
2) Electron gain or loss
Oxidation is the loss of electrons
Reduction is the gain of electrons