Chemistry Topic 6- Reversible Reactions Flashcards
How do reversible reactions reach equilibrium?
- As reactant react, their concentration fall- so the forward reaction will slow down. But as more products are made, and their concentrations rise, the backwards reaction will speed up
- After a while the forward reaction will be going at exactly the same rate as the backward one- the system is at equilibrium
What is a dynamic equilibrium?
When both reactions are still happening, but there is no overall effect because the concentrations of reactants and products have reached a balance and won’t change
What is the conditions needed so that equilibrium can be reached?
The reversible reaction has to take place in a ‘closed system’ (no reactants or products can escape and nothing can get in)
What does it mean when the equilibrium lies to the right?
The concentration of products is greater than the concentration of the reactants
(It is vice versa for if the equilibrium lies to the left)
What 3 things does the position of equilibrium depend on?
- Temperature
- Pressure (only involving gasses)
- Concentration (of reactants and products)
- If a reaction is endothermic in one direction, it will be exothermic in the other
- The energy transferred each way will be equal to one another
Write the equation for the thermal decomposition of hydrated copper sulfate
Hydrated copper sulfate anhydrous copper sulfate + water
*Hydrated copper sulfate anhydrous copper sulfate + water
Which way of the reaction is exothermic and which way is endothermic?
BACKWARDS reaction- EXOTHERMIC- this is because if you add a couple of drops of water to the white powder, you get the blue crystals back again
FORWARD reaction- ENDOTHERMIC- this is because if you heat blue hydrated copper(ll) sulfate crystals, it drives the water off and leaves white anhydrous copper (ll) sulfate powder
What is Le Chatelier’s Principle and what is it used for?
- It is the idea that if you change the conditions of a reversible reaction, the system will try to counteract that change
- it is used to predict the effect of any changes you make to a reaction system
TEMPERATURE
* if you decrease the temperature, the equilibrium will move in the exothermic direction
The equilibrium will move in the EXOTHERMIC direction to produce more heat
*this means that you’ll get more products for the exothermic reaction and fewer for the endothermic one
What does heating this reversible reaction do?
Ammonium chloride ammonia + hydrogen chloride
(HINT: the forward action is endothermic)
It moves the equilibrium to the right (more ammonia and hydrogen chloride)
What does decreasing the temperature of this reaction do?
N + 3H 2NH
2 2 3
(HINT: the forward reaction is exothermic)
It moves equilibrium to the right (more NH )
3
PRESSURE
*only affects equilibrium with gasses
What happens if you increase the pressure?
The equilibrium tries to reduce it so it moves in the direction where there are fewer molecules of gas
*you can use the balanced symbol equation for a reaction to see which has more molecules of gas
N +3H 2NH
2. 2. 3
What would happen if you increase the pressure?
The equilibrium would shift to the right, so you get more NH3
*this is because there are 4 moles on the left (1 of N2 and 3 of H2) but only 2 on the right
CONCENTRATION
What happens if you increase the concentration of the reactants?
The system tries to decrease it by making more products (the equilibrium shifts to the right)
N. +3H. 2NH
2. 2. 3
What happens if you add more N2 or H2?
The forward reaction increases to produce more NH3
