C8.1 - C8.9 - Rates And Equalibrian✔️ Flashcards
What happens when a reaction reaches equilibrium in a closed system?
At equalibrian the rate of the forward reaction equals the rate of the reverse reaction
What does it mean if a reaction is in a closed system?
Closed system - no reactants or products can get out
What is a reversible reaction?
The products of the reaction can react to re-form the original reactants
Define Le Châteliers Principle?
noticed that whenever a change in conditions is introduced to a system at equilibrium the postion of equalibrium shifts so as to cancel out the change - the change in conditions can be changes in concentration,pressure or tempertaure
Le Châteliers Principle states that changes in …….. effect the position of equalibrium?
the change in conditions can be changes in concentration,pressure or tempertaure which will shift the position of equalibrium
Why is Le Châteliers Principle important in the chemical industry?
Chemists need to find the conditions that give as much products as possible in the shortest time so it is economical
2 ways to work out the rate of a chemcial reaction?
-the reactants are used up as they make products
-the products of the reaction are made
Finding out what 2 things…. allows you to work out the rate of a chemical reaction?
by finding out how quickly:
-the reactants are used up as they make products
-the products of the reaction are made
How do you calculate the rate of reaction at a specific time on a graph?
Draw the tangent to the curve and caculate its gradient (change in y / change in x) - the steeper the gradient the faster the reaction
5 main factors which effect the rate of a reaction?
-temperature
-surface area of solid reactants
-concentration of reactants in solution
-pressure of reacting gases
-presence of catalyst
Explain the collision theory?
Reactions can only take place when the particles (atoms,ions,molecules) reactants come together - and bump into each other and collide with enough energy to cause a reaction to take place
Define what activation energy is?
The minimum amount of energy that particles must have before they can react
3 ways you can increase the chance of a reaction?
-increasing the concentration of reactants in solutions
-increasing pressure of reacting gases
-increasing surface area of solid rectants
How will temperature increase rate of reaction?
Increases the frequency of collisions and makes the collisions more energetic which will result in an increased rate of reaction becasue a higher proportion of particles have energy greater than the activation energy - because heating a substance transfers energy to its particles which means they move faster
Why does increasing the surface area increase the rate of reaction?
More particles of the solid are exposed and able to react at any given time and are in contact with reacting particles
Equation for working out the rate of a reaction?
Mean rate of reaction = quanity of reactant used / time
Effect of increasing pressure?
Increasing pressure of reacting gases also increases the frequeny of collisions and so increases the rate of reaction
Effect of increasing concentration?
Increasing concentration of reactants in solutions increases the frequency of collisions between the particles, and so increases the rate of reaction
What are catalysts?
Changes the rate of chemical reactions but are not used up during the reaction - different reactions need different catalysts (enzymes act as catalysts in biological systems)
How do catalysts increase the rate of a chemical reaction?
Catalysts provide a different pathway for the reaction that has a lower activation energy
What are 2 disadvantages of catalysts?
- often very expensive metals - gold, platinum and palladium
- catalysts will eventually become ‘poisoned’ so that they do not work anymore
What are 3 advantages of catalysts?
- better for the enviorment - less fossil fules used to create the high temperature normally needed
- more economical - cost less and less energy is needed
- not used up in the reaction - can be used to speed up a reaction over and over again
How do catalysts benefit the enviorment?
Catalysts can result in the ability to operate at lower temperatures so less fossil fuels are burnt and it also stops more carbon dioxide entering the atmosphere helping combat climate change
Explain how catalysts become ‘poisend’?
Impurities in the reaction mixture combine with the catalyst and eventually they stop working properly
What does changing the conditions result in for reversible reactions? give and example of the reaction with ammonium chloride?
The direction of the reversible reaction eg:
(heat) Ammonium chloride ⇌ ammonia +hydorgen chloride (cool)
If a reversible reaction is exothermic in one direction in the opposite direction it will be ….? Give an example using hydrated copper sulfate?
Endothermic with the same amount of energy transferred in each case
Example:
(endothermic) Hydrated copper sulfate ⇌ anhydrous copper sulfate + water (exothermic)
What is the result when a reversible reaction occurs in apparatus which prevents the escape of reactants and products?
Equilibrium is reached when the forward and reverse reactions occur at exactly the same rate
What happens if the concentration of one of the reactants or products is changed?
The system is no longer at equalibrium and the concentrations of all the substances will change until equilibrium is reached again
What happens if the concentration of a reactant is increased?
More products will be formed until equalibrium is reached again
What happens if the concentration of a reactant is decreased?
More reactants will react until equalibrium is reached again
What happens if the temperature of a system at equalibrium is increased in both exothermic and endothermic reactions?
- relative amount of products at equalibrium increased for endothermic reaction
- relative amount of products at equalibrium decreases for exothermic reaction
What happens if the temperature of a system at equalibrium is decrease in both exothermic and endothermic reactions?
- the relative amount of products at equalibrium decreases from an endothermic reaction
- the relative amount of products at equalibrium increases for an exothermic reaction
What is the effect of an increase in pressure on the position of equilibrium?
An increase in pressure causes the equlibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction
What is the effect of an decrease in pressure on the position of equilibrium?
A decrease in pressure cause the equalibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction
How can yoou change the relative amount of products formed at equalibrium?
Changing the temperatue at which you carry out the reversible reaction - you can plan to get more of the products and less of the reactants
What can Le Chatelier’s Prinicle be used for?
The effects of changing conditions on a system can be predicted using this principle
