rates of reaction (topic 6) Flashcards
a student is investigating the rate of reaction between magnesium and hydrochloric acid, state the independent variable in the students investigation
surface area of magnesium
the reaction produced 0.089 dm3 of gas in 90s, calculate the average rate of reaction for the reaction between magnesium and hydrochloric acid, give your answer in cm3/s to 2 decimal places (3)
write a balanced symbol equation for the reaction between sodium and water
the student plans another experiment, where they cut the 1 g of sodium into many small pieces before adding it to the water, the student claims that the rate of reaction will to be slower, are they correct, explain your answer with reference to collision theory (3)
- student is incorrect, rate of reaction would be faster with smaller pieces
- small pieces of sodium have a larger surface area to volume ratio than 1 g block
- the water and sodium will have a greater number of successful collisions or more frequent successful collisions
- rate of reaction will be higher
explain the effect of using warm water instead of cold tap water on the rate of reaction (3)
- water molecules have greater kinetic energy
- so particles move faster
- there are more frequent collisions between particles
- higher proportion of collisions have at least the activation energy to react when particles collide
write a balanced chemical equation to show the decomposition of hydrogen peroxide (H2O2) to form water and oxygen
state the test for oxygen gas
relight a glowing splint
explain the role of the solid manganese(IV) oxide in the reaction (3)
- solid manganese(IV) oxide acts as a catalyst
- increases the rate of reaction
- chemical formulae of reactants and products not affected by presence of catalyst or provides alternative route for reaction
- catalyst lowers the activation energy for reaction
describe a method to show that solid manganese(IV) oxide is a catalyst in this reaction, decomposition of hydrogen peroxide (H2O2)
- complete reaction without solid manganese(IV) oxide and record the time taken for the reaction to complete and volume of gas produced
- repeat with solid manganese(IV) oxide added
- (if solid manganese(IV) oxide is a catalyst), reaction will complete quicker without changing the volume of gas produced
describe what the student should expect to observe as the concentration of hydrochloric acid is increased (2)
- the reaction will finish more quickly
- because the rate of reaction will be higher
explain, with reference to particle theory, why increasing the concentration increases the rate of reaction (2)
- increasing the concentration increases the number of particles per volume
- resulting in more frequent collisions
- resulting in more successful collisions
- more collisions exceed the activation energy of the reaction
which of the following could be a possible change made by the student for trial 3:
- increased the concentration of hydrochloric acid used
- increased the mass of magnesium added
- decreased the temperature of the reaction
- decreased the mass of magnesium added
decreased the mass of magnesium added
after the experiment the student concluded that the quickest rate of reaction is obtained when they use high concentration of hydrochloric acid at a low temperature, do you agree, explain why (3)
- the students conclusion is only partially correct
- increasing the concentration will increase the rate of reaction
- but decreasing the temperature will reduce the rate of reaction
- as particles will have lower energy
- and move slower
- so there will be fewer successful collisions or fewer collisions will reach the activation energy
explain the role of a catalyst in a chemical reaction (2)
- catalysts increase the rate of reaction without changing the products of the reaction or increase the rate of reaction without getting used up in the reaction
- by providing an alternative reaction pathway
- and lower the activation energy of the reaction
describe how the student could improve the accuracy of their line of best fit, there is an anomalous result (2)
- repeat the anomalous result
- include a greater number of concentrations between 0.1 and 1.0 mol/dm3
- adds 50 cm3 of dilute hydrochloric acid to the conical flask.
- magnesium ribbon added to the conical flask and cotton wool inserted into the top of the flask
- recorded the mass loss every 20 s until the mass remained constant
