Reaction rate, collision theory and activation energy Flashcards
the rate of a chemical reaction is determined b the change
in concentration of a reactant or a product per unit time
rate of reaction=
(change in concentration) divided by (time for change to happen)
to measure the rate of reaction, we need to know (2 items)
- how fast one of the reactants in being used up
- how fast one of the products is being formed
in a graph displaying the concentration of a reactant against time, the gradient shows
the rate of reaction
we can see the reaction is complete when the gradient on a graph is = to
0, where the gradient is parallel to the x axis (flat)
when the curve on a graph is curved, we draw a………and use the equation Gradient=………….to find the rate of direction
tangent (straight line which touches the curve at on point) and Gradient= y / x to find rate of reaction
if the unit of concentration is moles per cubic decimetre, and time in secs, then the unit for rate will be
mol dm-3 s-1
the rate of reaction can also be calculated by measuring the time it takes for a known……………of product/ reactant to be…………/………………. and the equation rate=……………………….used
the rate of reaction can also be calculated by measuring the time it takes for a known AMOUNT of product/ reactant to be PRODUCED/USED UP and the equation rate= AMOUNT COLLECTED/USED UP / TIME TAKEN used
if it takes 40 seconds to collect 20 cm3 of gas, the the rate of reaction was:
rate= amount / time rate= 20 / 40 = 0.5 cm3 s-1
collision theory is the idea that
molecules have to collide in order to react, but even then a collision does not mean that a reaction will occur. the collision has to be successful in order to result in a reaction
the two requirements for a collision between two molecules to be successful are:
- the two molecules must collide with sufficient energy to cause a reaction (activation energy)
- the two molecules must collide in the correct orientation
activation energy is
the minimum energy that colliding particles must possess for a reaction to occur, E(a)
the symbol for activation energy is
E(a)
only collisions with equal or greater…………………will result in a reaction
activation energy
all chemical reactions involve (in terms of bonds)
breaking and making new bonds
breaking bonds ….energy while making new ones…………..energy
requires, releases for new bonds
activation energy is involved in
breaking some of the original bonds
where collisions are of relatively low energy, the bond-breaking process will
not occur
orientation affects whether a reaction will occur because
if two molecules collide so that the groups or atoms involved do not ‘touch’, then no reaction occurs. therefore collisions have to be of both high enough energy and correct orientation so that a reaction occurs
a ‘steric factor’ is when
the shapes of molecule influences reactions
‘steric hindrance’ in when
atoms or groups of atoms in the reacting molecule physically hinder the reaction through the blocking of attacking species
