Rate Of Reaction Flashcards
(25 cards)
What is the rate of a reaction?
The rate of a reaction is a measure of how quickly a reactant is used up, or how quickly a product is formed.
Why is it important to have a fast rate of reaction in the chemical industry?
In the chemical industry, faster rates of reaction can lead to more money being made.
According to collision theory, what does the rate of a chemical reaction depend on?
According to collision theory, the rate of a chemical reaction depends on:
1) The collision frequency of reacting particles.
2) The energy transferred during a collision.
What is collision theory?
Collision theory is the theory that chemical reactions only occur when particles collide with sufficient energy.
What factors can affect the rate of a chemical reaction?
Factors that can affect the rate of a chemical reaction include the temperature, the concentration of a solution/pressure of a gas, the surface area and the presence of a catalyst.
How would increasing the temperature affect the rate of a chemical reaction?
Temperature is a measure of the average kinetic energy of the particles that make up a substance. Thus, if the temperature were to be increased, the reactant particles would have more kinetic energy and so would move faster. This would lead to a higher frequency of collisions, increasing the rate of reaction.
How would increasing the concentration/pressure affect the rate of a chemical reaction?
If the concentration/pressure is increased, then there will be more reactant particles per unit volume. This will lead to a higher frequency of collisions, resulting in a higher rate of reaction.
How would increasing the surface area affect the rate of a chemical reaction?
If the surface area of one of the reactants is increased, then the reactant particles will have a greater area to collide with. This will result in a higher frequency of collisions, and so a higher rate of reaction.
What is a catalyst?
A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction.
How would using a catalyst affect the rate of a chemical reaction?
Catalysts provide an alternative reaction pathway for the reaction to occur that has a lower activation energy, which increases the frequency of successful collisions, causing a higher rate of reaction.
Give the units for rates of reaction.
The unit for rates of reaction can either be cm^3/s or g/s.
How can the rate of a chemical reaction can be measured?
The rate of a chemical reaction can be measured by:
1) Recording the visual change in a reaction (colour change or precipitation). This can be done by placing a cross underneath the test tube and measuring the time taken until it can no longer be seen. However, this is very subjective.
2) Measuring the change in mass (due to a gas being released). This is very accurate, but has the disadvantage of releasing the gas straight back into the room.
3) Measuring the volume of gas given off using a gas syringe.
What is the cloudiness of a solution a measure of?
The cloudiness of a solution is a measure of its turbidity.
Describe two methods in which the effect of changing the concentration of a reactant on the rate of the reaction is investigated.
Method 1:
1) Add a set volume of dilute HCl to a conical flask.
2) Place the conical flask on a mass balance.
3) Add a strip of magnesium to the acid and quickly plug the flask with cotton wool.
4) Start a stopwatch and measure the mass on the balance, taking readings at regular intervals.
5) Repeat steps 1-4 until three sets of concordant results are obtained, and calculate a mean.
6) Repeat steps 1-5 with more concentrated acid solutions.
7) Plot a graph of loss in mass (g) against time (s).
Method 2:
1) Add a set volume of dilute sodium thiosulphate to a conical flask.
2) Place the flask on a piece of paper with a black cross drawn on it.
3) Add a set volume of HCl to the flask and start the stopwatch.
4) Start a stopwatch and measure the time taken for the cross to disappear.
5) Repeat steps 1-4 until three sets of concordant results are obtained, and calculate a mean.
6) Repeat steps 1-5 with more concentrated acid solutions.
By using a graph, how can you find the rate of reaction at a particular point?
You can find the rate of reaction at a particular point by drawing a tangent on the graph at that point.
What sign is used to indicate that a reaction is reversible?
The ⇌ sign indicates that a reaction is reversible.
Define equilibrium.
Equilibrium is established when the rate of the forward reaction is equal to the rate of the reverse reaction.
It is important to note that at equilibrium, the reaction is still happening, but there is simply no overall effect (it’s a dynamic equilibrium).
Why can equilibrium only be reached in a closed system?
At equilibrium, all the macroscopic variables of the reaction have stopped changing. If matter and energy are being exchanged with the environment, then this cannot be the case.
What does ‘the position of equilibrium’ refer to?
The position of equilibrium refers to the proportion of reactants and products that exist at equilibrium. For example, if the position of equilibrium is to the left, then there will be more reactants than products at equilibrium.
What three factors can affect the position of equilibrium?
The position of equilibrium can be affected by the temperature, the pressure, and the concentration of the reactants and the products.
If the forwards reaction of a reversible reaction is exothermic, what will the reverse reaction be?
If the forwards reaction of a reversible reaction is exothermic, the reverse reaction will be endothermic.
What is Le Chatelier’s Principle?
Le Chatelier’s principle states that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.
How can changing the temperature of a reaction affect the position of equilibrium?
If the temperature of a reaction is increased, then the endothermic reaction will be favoured, and vice versa.
How can changing the pressure of a reaction affect the position of equilibrium?
Changing the pressure of a reaction will only affect the position of equilibrium of a reaction that involves gases.
If the pressure of a reaction is increased, the position of equilibrium will move to the side where there are fewer moles, and vice versa.
