Paper 2 (6) Flashcards
What does the rate of chemical reaction refer to?
The speed at which the reactants get turned into products
Give an example of a slow reaction
-> Rusting of iron
Give an example of a typical rate of reaction
Magnesium and acid produces a gentle stream of hydrogen bubbles
Give an example of a fast reaction
Explosions such as fireworks
To measure the rate of a reaction, we can either measure…
-> How fast the reactants are being used up
OR
-> How fast the products are being formed.
What are the two equations to work out rate of reaction?
Rate of reaction = quantity of reactants used/ time taken
OR
Rate of reaction = quantity of products formed/ time taken
cm3/s
g/min
Name four factors that affect the rate of chemical reactions.
Temperature
Concentration/ pressure
Surface Area
Catalyst
What does the collision theory state?
Collision theory states that for particles to react, they have to collide with sufficient energy.
The minimum amount of energy required for a reaction to take place is called the _________ energy.
Activation
When considering how a condition will affect the rate of reaction, you have to consider how it will affect the _________ of collisions, and/or the _________ of the particles.
frequency
energy
Explain how the rate of reaction changes with increasing temperature.
4 points
As temperature increases the particles gain kinetic energy, and so move around more quickly. This means that they collide more frequently, and with more energy. Therefore, there will be more collisions that surpass the activation energy, so the rate of reaction will increase.
Particles will have more energy
Particles will collide more frequently
More successful collisions
Higher rate of reaction
What does concentration/ pressure refer to?
Particles per unit of volume.
Concentration = generally solutions
Pressure = gases
What increases the frequency of collisions of the particles in a reaction? Give 2
Increasing the concentration
Increasing the temperature
Using powder instead of small chunks
A substance that increases the rate of a reaction without being chemically changed, or used up, is called a _________.
catalyst
What do catalysts do to the reaction energy?
Lowers the activation energy by providing an alternative reaction pathway.
Higher proportion of successful collisions.
Give three examples of catalysts:
Cobalt
Nickel
Enzymes
Should you include the catalyst in the chemical reaction as one of the reactants?
No
Do transition metals make good catalysts?
Yes
What is the equation to calculate the gradient?
change in y over change in x
(rise over run)
By finding the gradient of the tangent to a curve at a specific time, we can calculate the:
Rate of reaction at a specific time
During a chemical reaction, when is the rate normally fastest?
At the start
A line may be steepest at the start of a reaction because there are a lot of _________.
Over time, the line may become ____ steep as the reactants are _____ up.
At the end of the reaction, when all the reactants have been used up, the line p_______.
reactants
less
used
plateaus
You may sometimes hear the term d______ equilibrium rather than just equilibrium. They both mean the same thing, so you can use either.
dynamic
What is the correct symbol for a reversible reaction?
⇌
What is a reversible reaction?
A reversible reaction is one in which both the forward and reverse reactions can take place.
Give 2 statements about a system in equilibrium:
-> It requires a closed system
-> The concentrations of the reactants and products remain constant
-> The forward and backward reactions occur at the same rate
At equilibrium, if the concentration of reactants is higher than the concentration of products, we say that the position of equilibrium lies to the:
Left
What happens in an endothermic reaction?
Heat energy is taken in from the surroundings
In a reversible reaction, if the forward reaction is exothermic, the backward reaction is ___________.
endothermic
If the position of equilibrium lies to the right, it means there are more:
Products
In a reversible reaction, if the forward reaction is endothermic, what would be the affect of increasing the temperature?
Equilibrium would shift to the right
In a reversible reaction, if the forward reaction is exothermic, what would be the effect of decreasing the temperature?
Yield of products would increase
What is Le Chatelier’s Principle?
Le Chatelier’s principle states that if you change the conditions of a reversible reaction, the position of equilibrium will shift to try and counteract the change.
At equilibrium, if there are more products than reactants, we say that the position of equilibrium lies:
To the right
What are the three factors that affect the position of equilibrium?
Temperature
Concentration
Pressure
An increase in pressure moves the position of equilibrium to whichever side has the:
smaller number of gas molecules.
Le Chatalier’s principle states that if pressure is increased, equilibrium will shift to decrease the pressure. This means that equilibrium will shift to the side with less moles of gas as these will contribute less pressure.
In a reversible reaction, changes in pressure will only affect substances that are in the:
gaseous state
Le Chatalier’s principle states that if you increase the pressure, the position of equilibrium will shift to the side that _________ the pressure back down.
decreases
N2(g) + 3H2(g) ⇋ 2NH3(g)
In the above reaction, increasing the pressure will:
Shift the position of equilibrium to the right.
H2(g) + I2(g) ⇋ 2HI(g)
In the above reaction, increasing the pressure will:
Have no effect on the position of equilibrium
2NO2(g) ⇋ N2O4(g) (-24 kJ mol-1)
In the reaction above, the (-24 kJ mol-1) tells us that the forward reaction is:
Exothermic
2NO2(g) ⇋ N2O4(g) (-24 kJ mol-1)
In the above reaction, increasing the temperature will:
Shift the position of equilibrium to the left.
Le Chatalier’s principle states that if you increase the temperature, the position of equilibrium will shift to reduce the temperature. This means equilibrium will shift in the endothermic direction, which in this case is to the left.
N2(g) + 3H2(g) ⇋ 2NH3(g)
For the above reaction, increasing the concentration of nitrogen will:
Shift the position of equilibrium to the right.
Le Chatalier’s principle states that if you increase the concentration of a substance, the position of equilibrium will shift to reduce the concentration back down. This means that if you increase the concentration of nitrogen, equilibrium will shift to the right so that the concentration of nitrogen decreases again.
