Rate and extent of chemical change Flashcards
(28 cards)
What do we mean by the rate of reaction?
The quantity of the product or reactant formed/time taken
product or reactant = grams or cm3
time taken = seconds
What are the four main factors that affect the rate of reaction?
Temperature
Concentration/Pressure
Catalysts
Surface area
What is the collision theory?
Depends on two things: the frequency of collisions between reacting particles (increases the probability of successful collision) and the energy transferred during a collision (so more collisions are successful)
How does temperature affect the rate of reaction?
Particles have more energy so collide more frequently, collisions occur with more energy so more collisions have energy
How does concentration affect the rate of reaction?
changing pressure = changing concentration
High concentration = more particles per unit of volume, more frequent collisions
High pressure = particles are closer together per unit of volume so more frequent collisions
How does surface area affect the rate of reaction?
More reactants are exposed to other reactants to more frequent collisions
What is the rate of reaction directly proportional to?
The rate of reaction is directly proportional to the frequency of successful collisions
What is a catalyst?
A catalyst is a substance that speeds up a chemical reaction without being changed or used up in the reaction
How does a catalyst increase the rate of reaction?
By providing a different pathway for the reaction that has a lower activation energy
How do we work out the rate of a reaction?
Rate of reaction = amount of reactant used or amount of product formed/ time
How do you work out the rate of reaction through precipitate and colour change?
You can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution.
The quicker the mark disappears, the quicker the reaction
However, it can be subjective and you can’t plot a rate of reaction graph from the results
How do you work out the rate of reaction through change in mass?
Using a mass balance where you just place the reaction vessel on the balance and add the reactants to a conical flask and put a piece of cotton wool in the neck. As the gas is released, the mass disappearing is measured on the balance.
most accurate as the mass balance is very accurate but it has the disadvantage of releasing gas straight into the room
How do you work out the rate of reaction through the volume of gas given off?
Use a gas syringe to measure the volume of gas given off, the more gas given off during a give time interval, the faster the reaction
Gas syringes quite accurate but could be misread and have to be careful as if the reaction is too vigorous you can easily blow the plunger out of the end of the syringe.
What is a reversible reaction?
one where the products of the reaction can themselves react to produce the original reactants
What is an example of a reversible reaction
ammonium chloride ⇌ ammonia + hydrogen chloride
ammonium chloride is thermally decomposed to form ammonia and hydrogen chloride
Heating means that more of the products are produced whilst cooling means more of the reactants are produced
If a reversible reaction is exothermic in one direction…
it is endothermic in the opposite direction
the energy absorbed by the endothermic reaction id equal to the energy released by the exothermic reaction
What is an example of a reversible reaction that is endothermic in the forward reaction but exothermic in the reversed?
hydrated copper sulfate (blue) ⇌ anhydrous copper sulfate (white) + water
If a reversible reaction takes place in a closed system, then what state will always be reached?
Equilibrium
What is equilibrium?
When the amounts of reactants and products reach a balance - their concentrations stop changing
When a reversible reaction occurs in a closed system…
equilibrium is reached when the forward and reverse reactions occur at exactly the same rate
What is Le Chatelier’s Principle?
if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change
This means the effect of any changes to a system can be predicted
By altering what can you alter the yield of the reaction?
Temperature, pressure or concentration
If the temperature of a system at equilibrium is increased…
- the relative amount of products at equilibrium increases for an endothermic reaction
- the relative amount of products at equilibrium decreases for an exothermic reaction
If the temperature of a system at equilibrium is decreased…
- the relative amount of products at equilibrium decreases for an endothermic reaction
- the relative amount of products at equilibrium increases for an exothermic reaction
