C6 Rates Flashcards
What is the rate of a chemical reaction in terms of reactants?
How quickly the reactants in a reaction are used up
What is the rate of a chemical reaction in terms of products?
How quickly the products in a reaction are formed
What is the formula for a mean rate of reaction in terms of reactants?
quantity of reactant used/time taken
What is the formula for a mean rate of reaction in terms of products?
quantity of reactant product formed/time taken
How can you measure the quantity of a reactant or product?
In grams or in cm³
What are the possible units for rate of reaction?
g/s, cm³/s or mol/s (where s is seconds)
How could you measure the rate of a reaction from a graph?
Draw a tangent to the curve and calculate the gradient.
What is a tangent line?
A straight line that just touches the curve of best fit
How do you calculate a gradient?
change in values on y axis ÷ change in values on x axis
What is “collision theory”?
The theory that chemical reactions only occur when particles collide with enough energy
What factors can affect the rate of a reaction?
Temperature, surface area of a solid, concentration or reactants in solution, pressure of gases
State the effect of increasing the surface area on the rate of a reaction
Increases the rate
How can you increase the surface area of a solid?
Break it into smaller pieces.
Explain why increasing the surface area increases the rate of a reaction
More particles are available to collide, there are therefore more frequent collisions between reactants.
State the effect of increasing the concentration on the rate of reaction
Increases
Explain why increasing the concentration increases the rate of reaction
More particles in the same volume, therefore more frequent collisions between reactants.
State the effect on increasing the pressure of a gas on the rate of reaction
Increases
Explain why increasing the pressure of a gas increases the rate of a reaction
More particles in the same volume, therefore more frequent collisions between reactants.
State the effect of increasing the temperature on the rate of reaction
Increases
What is the activation energy?
The energy needed to break bonds to start a reaction
Explain why increasing the temperature increases the rate of reaction
Increases the kinetic energy of the particles so more frequent collisions, it also increases the number of particles which have the activation energy therefore more collisions result in a reaction.
What is a catalyst?
Something which changes the rate of a reaction but is not used up in that reaction
How do catalysts speed up reactions?
They provide another route for the reaction with a lower activation energy.
What is a reversible reaction?
A reaction which can go from reactants to products but also from products to reactants
What chemical symbol represents a reversible reaction?
⇌
If a reaction is exothermic in the forward direction what will it be in the reverse direction?
Endothermic
Two reactants require 30kJ to turn into products. What energy transfer is involved when the products turn into reactants?
30kJ is released
What is equilibrium?
When the forward and backwards reactions are occurring at the same rate in a closed system
How is the amount of reactant changing at equilibrium?
It is not changing
How is the amount of product changing at equilibrium?
It is not changing
What is Le Chatelier’s principle?
When a reaction at equilibrium is changed, it will seek to counteract that change
How does increasing the concentration of a chemical affect the equilibrium position?
The equilibrium will shift away from that chemical until it reaches equilibrium again
How does increasing the temperature of they system affect the equilibrium position?
The equilibrium shifts to the side with the least gas molecules until it reaches equilibrium again
How does increasing the pressure of they system affect the equilibrium position?
The equilibrium shifts to the endothermic side until it reaches equilibrium again
A reaction is exothermic in the forward direction. What will occur if the temperature is increased?
The backward reaction will increase as it is endothermic.
A reaction is at equilibrium when some product is removed. What will occur?
The forward reaction will increase as that will increase the amount of product
The reaction below is at equilibrium. What will occur when the pressure is increased? 2H₂(g) + O₂(g) ⇌ 2H₂O(g)
The forward reaction will increase as there are fewer molecules on the right.
