Chemistry paper exam questions 2 Flashcards
Reversible reactions can reach equilibrium in a closed system. What is a closed system
nothing can enter
explain why when a reversible reaction reaches equilibrium, the reaction appears to have stopped
because forward and backward reactions have the same rate and there is no overall change in the quantity of products and reactants
Name a natural resource from which hydrogen is produced.
natural gas
The Haber process uses a catalyst to speed up the reaction.
Explain how a catalyst speeds up a reaction
They speed up the reaction by reducing the activation energy (lower the activation energy) and providing a different pathway for the reaction
What happens to the amount of ammonia produced at equilibrium if the pressure is
increased?
Give a reason for your answer.
when the pressure is increased the equilibrium moves to the side of the equation with fewer moles of gas therefore the amount of ammonia increases
How does the diagram show that the reaction is endothermic?
the energy of the products is higher than the energy of the reactants
Suggest what effect, if any, increasing the temperature will have on the amount of
hydrogen iodide at equilibrium.
Give a reason for your answer.
the amount of hydrogen iodide decreases and the equilibrium moves in the direction of the endothermic reaction.
Suggest two reasons why all of the points do not lie on the line of best fit
results not recorded correctly
plotting error
In a conclusion to the investigation, the student stated that:
‘The rate of this reaction is directly proportional to the concentration of the sodium
thiosulfate solution.’
How does the graph support this conclusion?
the graph goes in a straight line
Explain, in terms of particles, why the rate of reaction increases when the
the concentration of sodium thiosulfate is increased.
The particles are closer and collide more successfully
Explain, in terms of particles, why temperature has this effect on the rate of reaction.
To gain full marks in this question you should write your ideas in good English.
Put them into a sensible order and use the correct scientific words.
increasing the temperature increases the rate of a reaction because the particles can move faster as they have more energy and between the particles increase. Therefore more particles have activation energy.
State one variable that must be kept constant to make this experiment a fair test.
the rate of stirring
Phosphoric acid is made by reacting phosphate rock with sulfuric acid.
Only three of the methods shown below will increase the rate of this reaction.
Put a tick next to each of the three methods that will increase the rate of this reaction.
- use a more concentrated solution of sulfuric acid
- Grind the phosphate rock into a powder before adding the acid
- increase the temperature of the sulfuric acid
Information about car engines. Complete the sentence with the correct word
The exothermic reaction makes the temperature of the engine increase.
This is because during the exothermic reactions energy is given out to the surroundings.
The equation for the reaction that takes place in part A is:
2NO → N2 + O2
Which one of the substances shown in the equation is a compound?
Give the formula of this compound.
2no
why is it important to stop carbon monoxide from being released into the air
harmful
The table lists some statements about catalysts. Only two statements are correct
a catalyst can speed up a chemical reaction.
Different reactions need different catalysts.
Modern catalytic converters contain nanosized particles of catalyst.
Less catalyst is needed when nanosized catalyst particles are used.
Complete the sentence
The size of nanosized particles is smaller than normal sized
particles.
The catalysts contain platinum.
Suggest why a manufacturer of catalytic converters would want to use less catalyst.
save resources
The teacher said that the student should repeat the investigation to get more results.
Suggest why.
to make it accurate
The rate of reaction between sulfuric acid and phosphate rock can be increased if the
mixture is heated to a higher temperature.
Explain, in terms of particles, why an increase in temperature increases the rate of
reaction.
particles move faster and have more energy
State one other way in which the rate of reaction between sulfuric acid and phosphate rock
can be increased.
adding a catalyst
The equation for the reaction is:
Na2S2O3(aq) + 2 HCl(aq) → 2 NaCl(aq) + H2O(l) + SO2(g) + S(s)
(a) Explain why the solution goes cloudy.
because sulfur forms which is a solid
Describe and explain, in terms of particles and collisions, the effect that increasing
the concentration of sodium thiosulfate has on the rate of the reaction
The reaction rate increases as more reacting particles there are because the more particles increase the number of collisions also increases.
Complete the word equation for the reaction of sulfur dioxide with oxygen.
sulfur dioxide + oxygen – sulfur trioxide
Draw a ring around the correct answer to complete the sentence.
Sulfur dioxide (SO2) is
a compound.(the correct answer)
an element.
a mixture.
The reactants are gases.
When the pressure of the gases is increased, the reaction gets faster.
Complete the sentence.
When the pressure of the gases is increased,
the frequency of the collisions increases.
The particles need the energy to react.
Complete the sentence.
The minimum amount of energy that particles need to react is called
the activation energy.
Give one way of increasing the rate of the reaction other than changing the pressure.
by adding a catalyst
What volume of gas has been collected?
Volume = 36 cm3
What are two possible reasons for the anomalous result?
The bung was not pushed in firmly enough.
The measuring cylinder was not completely over
the delivery tube
Describe the pattern the graph shows up to 0.4 g of lithium carbonate added.
As the mass of lithium carbonate increases the volumes of gas increase ( linear proportional )
The equation shows the decomposition of lithium carbonate.
Li2CO3 (s) → Li2O (s) + CO2 (g)
Figure 4 shows the apparatus a student used to decompose lithium carbonate.
Why does the limewater bubble?
carbon dioxide is produced
The student repeated the experiment with potassium carbonate.
The limewater did not bubble.
Suggest why there were no bubbles in the limewater.
potassium carbonate does not decompose to produce carbon dioxide
State one conclusion the student could make about the effect of temperature on the
rate of the reaction.
the higher the temperature, the faster the reaction
Give one reason why the student could make this conclusion
40 degrees Celsius line becomes a horizontal line sooner than 20 degrees Celsius.
Which two variables should the student keep constant?
- concentration of acid
- mass of marble chips
Explain, in terms of particles and collisions, the effect that increasing the surface area
of the marble chips has on the rate of reaction.
increases rate because the particles are more likely to collide
Calcium carbonate is a catalyst for the industrial production of biodiesel.
Give one reason why using a catalyst reduces costs.
increases the rate of the reaction
The equation for the reaction is:
Na2S2O3(aq) + 2 HCl(aq) 2 NaCl(aq) + S(s) + SO2(g) + H2O(l)
Name the product that made the mixture go cloudy.
sulfur
Describe the trends shown in the student’s results.
the rate of reaction increases slowly (from 20 °C to 50 °C)
then increases more rapidly
Suggest two variables the student would need to control to make sure that her
results were valid.
they need to control the temperature of the reactants and the amount of sodium thiosulfate
From this investigation the student correctly concluded:
‘As the concentration of sodium thiosulfate solution doubles, the rate of reaction
doubles.’
Explain the student’s conclusion in terms of particles
because the concentration increases the particles are together and the reaction rate increases. Therefore the frequency of collisions increases so the frequency of collisions doubles.
A student investigated the rate of reaction between marble chips and hydrochloric acid.
Figure 1 shows the apparatus the student used.
What is A?
cotton wool
The equation for the reaction is:
2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l) + CO2(g)
Explain why there is a loss in mass in this investigation.
because there is a gas produced which escapes from the flask
The student measured the change in mass of the reactants.
Describe another method, other than measuring the change in mass of the reactions, that
the student could have used to find the rate of the reaction between marble chips and
hydrochloric acid.
the other methods could be counting the bubbles or collecting the gas in a gas syringe
Another student planned to investigate the effect of temperature on the rate of reaction.
The student predicted that the rate of reaction would increase as the temperature was
increased.
Give two reasons why the student’s prediction is correct.
The particles have more energy.
The particles move faster.
Marble chips are mainly calcium carbonate (CaCO3).
A student investigated the rate of reaction between marble chips and hydrochloric acid (HCl).
Figure 1 shows the apparatus the student used.
Figure 1
(a) Complete and balance the equation for the reaction between marble chips and hydrochloric
acid.
…..caco3…………. + ……2hcl………… → CaCl2 + …..h20…………. + ……….c20……..
Explain, in terms of particles, how and why the rate of reaction changes during the reaction
of calcium carbonate with hydrochloric acid.
the acid particles are used up so the concentration decreases, this means that there is less frequent collisions per second and the rate of the reaction slows down
Explain why the solution goes cloudy.
because of sulfur which is a solid
Give two variables the student must control to make the investigation a fair test.
- concentration of sodium thiosulfate
- concentration of hydrochloric acid
State the effect that increasing the temperature of the sodium thiosulfate solution has on
the rate of the reaction.
Explain this effect in terms of particles and collisions.
Increasing the temperature increases the rate of the reaction because particles have more energy, therefore, increasing the frequency of collisions between the particles. Additionally, more particles have energy greater than the activation energy
