rate of reaction Flashcards
RG p59-64
from educake
6g of a substance are pruduced from a reaction. 2.5g of platinum are added at the start of the reaction to be used as a catalyst. How much platinum will there be at the end of the reaction?
2.5g
calalysts do NOT get used up in reactions - they remain “chemically unchanged”.
from educake
Which answer best explains why a reaction slows down over time:
* the reactant particles lose energy and so there are less frequent collisions
* the amount of reactants decreases and there are less likely collisions
* the concentration of the reactants decreases and there are less frequent collisions
* the reactant particles lose engergy so there are less successful collisions ?
The concentration of the reactants decreases and there are less frequent collisions.
because…
As the reaction progresses, the reactants are consumed, leading to a decrease in their concentration. According to collision theory, a lower concentration of reactants results in fewer collisions per unit time, which in turn slows down the reaction rate.
from educake
on a “volume of product against time” graph, the steeper the line, the — the rate of reaction
steeper line = faster rate of reaction
from educake
In an experiment, marble chips reacted with dilute hydrochloric acid and carbon dioxide gas was given off.
The experiment was done twice, once using small marble chips and again with large marble chips.
Explain which reaction would happen quicker.
small marble chips = faster reaction:
* smaller marble chips would have a greater surface-area-to-volume ratio
* the greater the surface area to volume ratio, the faster the rate of reaction
* so the reaction with smaller marble chips will have a faster rate of reaction.
from educake
Does decreasing the temperature increase the rate of a reaction?
Increasing the temperature increases the number of successful collisions between reacting particles.
This is because the particles have more kinetic energy.
from educake
the smaller an object, the — surface area to volume ratio
The smaller an object, the higher the surface area to volume ratio.
(because surface area is proportional to the width squared, but volume is proportional to the width cubed, so volume increases faster than surface area when an object gets bigger.)
from educake
the higher the concentration, the — the rate of reaction
the faster the rate of reaction
from educake
Does increasing the surface area of a solid reactant increase, decrease or have no effect on the frequency of collisions between the reacting particles?
INCREASE:
Increasing the surface area increases the frequency of collisions between reacting particles because more reactant particles are exposed.
from educake
In order to react colliding particles must have energy…
* exactly equal to the activation energy
* less than or equal to the activation energy
* greater than or equal to the activation energy ?
greater than or equal to the activation energy
from educake
A catalyst provides a different — for a reaction with a — activation energy for a reaction.
A catalyst provides a different pathway for a reaction with a lower activation energy for a reaction.
from educake
True or false? Only a small amount of a catalyst is needed to catalyse large amounts of reactants.
True
Catalysts are not used up i.e. remain chemically unchanged during a reaction, so a small amount of catalyst can catalyse large amounts of reactants.
from educake
True or false? You can follow the progress of a reaction that produces a gas using a sensitive mass balance, because the mass of the reaction vessel increases as the gas is produced.
False - the mass of the reaction vessel will decrease as the gas produced leaves the reaction vessel.
what is the Law of Conservation of Mass?
the Law of Conservation of Mass states that the total mass before and after a reaction should remain constant.
from educake
In reaction 1, 12g of reactants were converted to products in 30 seconds. In reaction 2, 200g of reactants were converted to products in 8 minutes. Which reaction happened at the faster rate?
rate = (volume of reactants used or products formed) / (time)
Rate for reaction 1 = 12 ÷ 30 = 0.4 g/s
Rate for reaction 2 = 200 ÷ 480 = 0.42 g/s
so reaction 2 has a faster rate
(8 minutes converted into 8 × 60 = 480 seconds)
from educake
how can you tell from (the shape of) a graph when the reaction has stopped?
the graph levels off/plateaus because:
1. all pf at least one of the reactants has been used up
and:
2. all the product has been formed (and no more will be formed)
