Rates Of Reactions Flashcards
Define rates of reaction
Rate of reaction is the change in the concentration per unit of time of any one reactant or product
How are rates of reaction measured?
the formation of a product per unit time can be measured
the loss of a reactant per unit time can be measured
How to calculate average rate of reaction?
Average rate of reaction = Amount of substance formed or lost/ time taken for that to happen
What is ment by instantaneous rate of reaction
the rate of a reaction at any one particular time during the reaction
how to find instantaneous rate of reaction from a graph
draw a tangent to the curve at time asked
choose two good points.
find slope using formula
What dertimes weather a reaction does or does not take place
Reactants will collide with each other when mixed.
These reactats have a certain amount of energy.
if the colliding reactants meet the required energy(acivation energy) it will be an effective collision
What is activation energy
The minium combined energy of colliding particles for effective collisions/ for an reaction to take place
What is mean by an effective collision
A collision that reached activation energy and results in the formation of products
Draw out an large activation energy reaction profile diagram
reactants
large activation energy = slow rate of reaction
activation energy (Eact)
products
delta H
Describe the energy of products vs reactants in an exothermic reaction
energy of products is less than energy of reactants
ΔH = Energy of products – Energy of reactants
(ΔH will be a negative value)
Describe the energy of products vs energy of reactants in an endothermic reaction
energy of products is greater than energy of reactants
ΔH = Energy of products – Energy of reactants
(ΔH will be a positive value
Name the 5 factsots affecting the rate of a reaction
1-Nature of reactants
2-Particle size
3-Concentration
4-Temperture
5-Catalyst
Describe the nature of the reactants (Type of bonding) that occours involving ionic compounds in solution
Reactions involving ionic compounds in solution are faster.
-In solution, ionic compounds are dissociated, preset as free ions.
No bond breaking is required, the activation energy is lower.
Describe the nature of the reactants (Type of bonding) that occours involving covalent compounds in solution
Reactions involving covalent compounds have slower reactions
-Covalent compounds are not dissociated.Their bonds need to be broken and new ones reformed, The activation energy is higher
How does particle size affect the rate of a reaction, and explain why
Smaller particle size increases rate of a reaction
Larger size decreases the rate of a reaction
Reason
Smaller particles have a greater surfance area, meaning greater frequency of collisions occour, means that there will be more effective collisions- more collisions reach activation energy
Dust explosions present a risk in industry, Give five conditions necessary for a dust explosion to occour
particles must be combustible
dust particles must be dry
a source of ignition
Oxygen must be present
must be in an enclosed space
How does concentration of reactants affect the rate of a reaction, explain the reason
Increasing concentration increases rate of reaction
Decreasing concentration decreases rate of a reaction
-More concentrated solution has a greater number of particles.
Greater number of particles means greater frequency of collisions will occur, meaning more effective collisions will occour. More collision reach the required activated energy
What is the relationship between Concentration and the rate of reaction
directly proportional
Why does the rate of a chemical reaction generally decrease with time
as reaction proceeds, more reactants are used up, concentration decreases. Less frequecy of collisions, less effective collisions, less collisions reach activation energy
In the expeirment showing the effect of particle size of calcium carbonate in HCl, describe the difference between whole marble chips vs ground marble
smaller particle size - had a greater rate of reaction, steeper slope. The smaller particle size levels off first( reaction finishes off first)
Both the reactions rise to the same height eventially- both produce the same amount of product.
In the expeirment showing the effect of concentration on rate of reaction between calcium carbonate and HCl, describe the difference between 2 M HCl and 1M HCl
The Higher conc of HCl - higher conc reaction has a greater rate of reaction. The higher concentration reaction levels off first (finishes first) Reactions with double concentration of reactant rise to twice the height - produce twice as much product
How does temperture affect the rate of a reaction and explain the reason.
Increasing temerture increases the rate of reaction.
Decreasing temperture decreases the rate of an reaction
1.Increasing temp increases the energy of the particles (More effective collisions - more collisions reach required activation energy)
2. Increasing temp also increases velocity of collisions (greater frequency of collisions will occour - more reach reuired activation energy)
Given the two reasons why temperture increases the rate of reaction, which is more significant? Explain
Increasing the energy of the particles.
The increase in velocity is small compared to the substantial increase in energy in the particles ( which cause more effective collisions)
What effect does increasing/decreasing temperature have on the activation energy of a reaction?
None