Chapter 8 Flashcards
What is activation energy (Ea) ?
The minimum energy needed to start a reaction
What is a catalyst?
A substance that increases the rate of a chemical reaction. It is not used or changed in the reaction. It lowers the activation energy by finding an alternative pathway for the reaction
What is collision theory?
An explanation of chemical reactions that says that; particles must collide colliding particles have to have a sufficient amount of energy (Exceed the activation energy) in order for a reaction to take place
How can you find the rate of reaction?
Monitor the amount of reactants used up or products produced over time
How do you find out the rate of reaction from a graph?
The gradient of a line at any given time The Steeper the gradient the faster the reaction
What is rate of reaction given as a formula?
Mean rate of reaction = quantity of reactant used or quantity of product formed / time
What effect does surface area have on the rate of reaction?
The rate of reaction increases if the surface area to volume ratio increase. A larger surface area the more chance of a collision
What effect does temperature have on the rate of reaction?
Particles collide more frequently and more energetically so more particles have energy that exceeds the activation energy
What effect does pressure have on the rate of reaction?
It increases the frequency of collisions as you have a higher number of particles in a given volume
What effect does concentration have on the rate of reaction?
It increases the frequency of collisions as you have a higher number of particles in a given volume
What is a reversible reaction?
The products of the reaction can react to produce the original reactants
What does this show?
A reversible reaction
What does dynamic equilibrium mean?
In a closed system the rate of the forward reaction equals the rate of the reverse reaction
What is Le Chatelier’s principle?
The rule is that any change made to a reaction which is in equilibrium will result in the equilibrium position moving to minimise the change made
What does increasing the temperature do to the position of the equilibrium?
Increasing the temperature always favours the endothermic reaction. Decreasing the temperature always favours the exothermic reaction
What does pressure do the position of the equilibrium?
If there is at least one gas present in the equilibrium mixture, then a change in the pressure may affect the position of the equilibrium.
If the pressure increases the equilibrium will shift to the side with the fewest moles of gas.
Changes in pressure will not affect the position of equilibrium if the number of moles of gases on both sides of the equation are equal
What effect does a catalyst have on the position of the equilibrium?
A catalyst reduces the time taken to reach equilibrium but does not change the position of the equilibrium. This is because the catalyst increases the rates of the forward and reverse reactions by the same amount
Sketch a graph of the effect of concentration on the rate of reaction.
In the black cross method for determining the rate of reaction which product forms a precipitate?
The sulfur
HCl + sodium thiosulfate ————-> sodium chloride + sulfur dioxide + sulfur + water.
2HCl(aq) + Na2S2O3(aq) ————> 2NaCl(aq) + SO2(g) + S(s) + H2O(l)
Give a method to measure the rate of reaction if a gas is generated?
Use a gas syringe
