CHAPTER 8 RATES OF REACTION AND EQUILBRIUM Flashcards
Mean rate of reaction equation
Mean rate of reaction(g or cm^3/s) = quantity of reactant used(g or cm^3) / time taken(s)
3 things what lead to no reaction or reaction
1.reactants moving to slowly - molecules bounce(no reaction)
2.reactants not facing right way - molecules bounce(no reaction)
3.reactants collide in correct direction and with sufficient energy - successful collision(chemical reaction)
What is the collision theory
Chemical reactions can occur only when reacting particles collide with each other in the correct direction and sufficient energy. There is a minimum amount of energy that particles must have to react called the activation energy.
5 ways to increase the rate of reaction
1.increase the surface area of a solid
2.increase the concentration of a solution
3.increase the pressure of a gas
4.increase the temperature of the reactants
5.catalysts
Method of investigating the effect of concentration on rate of reaction
1.set up a syringe using a stand and clamp
2.cut a 3cm length of clean magnesium ribbon
3.add the magnesium ribbon to the hydrochloric acid, attaching the delivery tube straight away and starting the timer
4)record the volume of gas formed in 20 seconds
5)repeat the experiment with other concentrations if acid using a new piece of magnesium each time
What affect does increasing the size of pieces of a reacting solid have on the rate of reaction
Increasing the amount of pieces will increase the surface area meaning the surface area to volume ratio decreases causing the rate of reaction to increase as theres more chances for the reactants colliding in the correct direction with more sufficient energy as the surface area to volume ratio is decreased.
Why does increasing the concentration of a solution increase the rate of reactikn
As when you increase the concentration it increase the number of particles per cm^3 so it increases the frequency of collisions so then it increases the rate of reaction.
Investigating how temperature affects the rate of reaction method
- Measure 5cm^3 of hydrochloric acid into a conical flask standing on a crosss
2.collect 40cm^3 of the sodium thiosulfate in a boiling tube and record its temperature
3.add the sodium thiosulfate to the acid and immediately start timing
4.stop timing as soon as the cross is no longer visible
How does changing the temperature affect the rate of reaction
Increasing the temperature will increase the kinetic energy of the particles making them move faster so it increases the energy and frequency of of successful collisions therefore increasing the rate of reaction
What is a catalyst
A chemical which speeds up the rate of reaction but remains unchanged.
Catalysts in order of effectiveness in the temperature investigation
Most to least:
Copper(II) sulfate
Cobalt(II) chloride
Nickel(II) sulfate
Iron(II) sulfate
What are reversible reactions
When in some chemical reactions the products of the reaction can react to produce the original reactants
What is a closed system
Apparatus which prevents the escape of reactants and products
What is equilibrium
When the forward and reverse reactions occur at exactly the same rate
What happens in equilibrium ( 3 parts)
If increased:
The relative amount of products at equilibrium increases for an endothermic reaction and the relative amount of products at equilibrium decreases for an exothermic reaction
If decreased:
The relative amount of products at equilibrium decreases for an endothermic reaction and the relative amount of products at equilibrium increase for an exothermic reaction
What is the affect of changing concentration when a system is at equilbrium
- the system is now no longer at equilibrium and the concentration of all 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( moves to right hand side of equation)
-if the concentration of a product is decreased more reactants will react until equilibrium is reached again(moves to left hand side of equation)
The effect of temperature changes on equilibrium
If increased:
The relative amount of products at equilibrium increases for an endothermic reaction and the relative amount of products at equilibrium decreases for an exothermic reaction
If decreased:
The relative amount of products at equilibrium decreases for an endothermic reaction and the relative amount of products at equilibrium increase for an exothermic reaction and the
The effect of pressure changes on equilibrium
For gaseous reactions:
An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction.
A decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction.
