C8 Flashcards
Describe how you measure the mean rate of reaction ?…
Mean rate of reaction =
Quantity of reactant used / time
Or
Quantity of producted formed / time
On a graph showing the rate of reaction (x axis is time Y axis is amount of product) will the line be steep or less steep when the rate decreases in speed?
Less steep
On a graph showing the rate of reaction how would you caculate the rate of reaction at a specfic point?
Specfic point = draw a tangent at the specfic point and calculate the gradient
What does collision theory explain?
Collision Theory explains how various factors effect the rate of reaction.
Eg increasing concentration of reactants in solution, the pressure of reacting gases, or the surface area of solid reactants - increases the collision frequency of reacting particles
Eg increasing the temperature increases the frequency of collisions and makes the collisions more energetic - increases the energy transfered during a collision
According to this theory, chemical reactions occour, only when there is suffcient energy. (Activation energy).
How can the rate of a chemical reaction be increased and how do these achieve this ?
What do all of these increase to increase the rate of chemical reactions?
-increasing the concentrations of reactants in solution :
increase the frequency of collisions as there are more particles in the same volume
-increasing the pressure of reacting gases:
Increases frequency of collisions because the same numeber of particles occupie a smaller space
-decreasing the surface area of solid reactants:
Increasing SA:V increases frequency collision because the particles have a larger area to work on for the same volume of solid
-the temperature:
Colldide more frequently with more energy because the particles move faster
-the presence of catalysts:s
Decrease the activation energy by providing an alternative reaction pathway
All these increase the number of successful collisions between reacting particles
RP
RP
What is defintion of a catalyst?
Catalysts change the rate of chemical reactions but are not used up during the reaction and as such remain chemically unchanged
How does a catalyst speed up the reaction
Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.
How will a reaction profile for a catalyst look?
It will have a lower activation energy
How do you reach a (dynamic) equilbrium in a chemical reaction?
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 is the defintion of a reversible reaction and how does it reach equlibrium
A reaction where the products of the reaction can react to produce the original reactants.
E.g.
A+B - > C+D
As the reactants react thier concintraction falls but as more products are made thier concintration rises so the backwards reaction speeds up.
If thé forward reaction in a chemical reaction is exothermic what will the backwards reaction be and how much energy will be tranfered?
If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case.
What is Le Chatelier’s principle
If a reversible reaction is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.
What happens when the concintration of the reactants or products is changed in a system at equlibrium?
What heppens with:
Increased reactants
Increased products
If the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.
If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
If the concentration of a product is decreased, more reactants will react until equilibrium is reached again.
What will happen if If the temperature of a system at equilibrium is increased or decreased?
The conditions havé changed and the position of equlibrium will move in such a way as to counteract the change
If the temperature of a system at equilibrium is increased:
The equlibrium position will move in the endothermic direction
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 equlibrium position will move in the exothermic direction
the relative amount of products at equilibrium decreases for an endothermic reaction
the relative amount of products at equilibrium increases for an exothermic reaction.
