Chemistry exam Flashcards
a student investigated the reaction between magnesium and hydrochloric acid. give two observations the student could make during the reaction
- effervescence
- exothermic
the student investigated how the rate of this reaction changed when the concentration of hydrochloric acid was changed
firstly, using a concentration of 0.25mol/dm3 of HCl time how long it takes from when the magnesium is added to the HCl to the end of the reaction. This measures the rate of the reaction. To make the experiment a fair test use the same volume of hydrochloric acid. Repeat reaction twice with 0.1 and 0.5 mol/dm3 of hydrochloric acid
name the product that made the reaction go cloudy
sulphur
describe trends shown in the students results
as temperature increased relative rate of reaction also increased
student investigated the effect of changing the concentration of sodium thiosulfate solution on therate of reaction.
suggest two variables the student would need to control to make sure that her results were valid
-the volume of sodium thiosulfate must stay the same
from this investigation the student correctly concluded
‘As the concentration of sodium thiosulfate doubles, the rate of reaction doubles.’
explain the students conclusion in terms of particles
- if concentration increases there is a greater frequency of successful collisions.
- Particles are closer together
explain what is meant by equilibrium
the forward reaction and backward reaction occur at the same rate
how would increasing the temperature change the yield of ethanol at equilibrium?
give a reason for your answer
increasing the temp would decrease the yield of ethanol as the equilibrium favours the endothermic reaction
how would increasing the pressure change the yield of ethanol at equilibrium?
give a reason for your answer
increasing the pressure would increase the yield of ethanol because the equilibrium favours the side of the reaction with less moles
a catalyst is added to increase the rate of a reaction
explain how adding a catalyst increases the rate of a reaction
a catalyst increases the rate of a reaction because less energy is needed to complete the reaction. So it has a lower activation energy with a catalyst
explain, as fully as you can, why the average rate between 30 and 50 seconds is different from the rate between 0 and 10 seconds
As the reaction continues the concentration increases
a high pressure (between 50 and 100 atmospheres) is used in this process.
explain why the highest equilibrium yield of methanol is obtained at a high pressure
because as pressure increases the equilibrium moves to the side of the reaction with less moles
the temp ised in this process is about 250C
it has been stated that, ‘the use of this temperature is a compromise between the equilibrium yield of product and rate of reaction’
explain this statement
-this is because with a low temperature there is a good yield but a slower rate of reaction
which sub-atomic particles are present in the nucleus of an atom?
- protons
- neutrons
there are two isotopes of the element chlorine:
describe, in terms of sub-atomic particles
similarity: the number of protons
difference: the number of neutrons