C8 Flashcards
What is the rate of a chemical reaction?
How fast the reactants are changed into products
What is the slowest chemical reaction?
Rusting of iron
How to find the speed of a reaction?2 ways
- record the amount of product formed
- the amount of reactant used up over time.
What type of line would it be for a quick reaction?
A steep line
What does the rate of reaction depend on?
- temperature
- concentration of solution or pressure of gas
- surface area
- presence of a catalyst
How collisions affect the rate of reactions?
- collision frequency (how often they collide) more collisions means a faster reaction.
- energy transferred during a collision. Enough energy must be there for a collision to be successful
What is activation energy?
Minimum amount of energy that particles need to react. Particles need that much energy to break bonds in the reactants and start the reaction.
How does temperature effect the rate of reaction?
-increase , will increase the rate as particle move faster as have more energy (enough for reaction to happen) and will collide more frequently
How concentration or pressure affects the rate of reaction?
- increase in conc. will increase the rate of reaction as it mean more particles colliding in the same volume
- if the pressure of gas is increased , the same applies
- both of these increasing makes collisions between particles more frequent
How the surface area affects the rate of reaction?
- if there is a solid . Breaking it up into smaller bits will increase the surface area to volume ratio.
- same volume of solid will have more area for particles to collide amd so collisions will happen more frequently
How catalysts effect the rate of reaction?
They decrease activation energy needed for a reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy.
What is a catalyst?
Substance that speeds up a chemical reaction, without it being used up itself. It isn’t part of the overall equation. Different reactions need different catalysts.
What are enzymes?
Biological catalysts
Equations for the mean rate of reaction?
Quantity of reactant used / time taken
Quantity of product formed / time taken
How can the rate of a reaction be found?
Measuring the quantity of a reactant used or the quantity of the product formed over time.
How can the quantity of a reactant be measured?
Mass( gram) or volume (cm cubed)
What is the unit for rate of reaction?
g/s or cm ^3 /s
How to calculate the mean reaction from a graph?
Find the time taken and the volume or mass of the product and draw lines up to see what is the difference then divide thta by time taken.
Steps to draw a tangent to find the reaction rate at a particular point?
- position ruler on a given point
- adjust ruler so space is equal on both sides
- make tangent
- find the gradient of the line
How to work out the gradient of a line?
Change in y / change in x
What is a reversible reaction?
The products of the reaction can react to produce the original reactants .
How do you know if a reaction is reversible ?
If there is two arrows pointing opposite ways on top of each other.
How do reversible reactions react?
1) as reactant react , concentration of the forward reaction will slow down , so as more products are made the backwards reaction will speed up .
2) eventually it will be going at exactly the same rate which is the equilibrium
What is the equilibrium?
When a reversible reaction happens occurs in apparatus which prevent the escape of products or reactants, equilibrium is reached when the forward and reverse reactions occur at exactly the same time.
What happens if a reversible reaction is exothermic in one direction?
It is endothermic in the other directions.
For example :
Hydrated copper is endothermic forming copper sulfate + water but is exothermic on the way back .
How can the directions of a reversible reaction be changed?
Heating and cooling for example heating ammonium chloride will reach ammonia + hydrogen chloride and cooling will go the other way
Examples of endothermic and exothermic reversible reaction?
Hydrated copper sulfate reversible anhydrous copper sulfate
—–> endothermic
What are la chanteliers principles?
If you change the conditions of a reversible reaction at equilibrium , the system will try to counteract that change. It can be used to predict the effect of any changes you make to a reaction
What happens if the temperature increases in a reversible reaction?
- relative amount of products at equilibrium increases for endothermic reaction
- relative amount of products at the equilibrium decreases for exothermic
What happens to a reversible reaction if the temperature increases?
- relative amount of products at equilibrium decreases for endothermic
- relative amount of products at equilibrium increases for exothermic
What are the effects of changing concentration of a reversible reactants products or reactants?
System no longer at equilibrium and the concentration of all substances will change until at the equilibrium again.
What happens in a reversible reaction if the concentration of the reactant increases?
More products will be formed until equilibrium is reached
What happens if the concentration of a product is decreased in a reversible reaction?
More reactants will react until equilibrium is reached again
What state does pressure affect?
Gaseous state
What will happen if there is an increase in pressure in a reversible reaction ?
The equilibrium position will shift towards the side with smaller number of moles as shown by the symbol equation for that reaction
What will happen if there is a decrease in pressure in a reversible reaction?
Causes the equilibrium to shift towards the side with the large number of moles as shown by the symbol equation.
