Rates of Reaction Flashcards
All 24 cards in this deck
What are the steps to measure the rate of reaction between hydrochloric acid and marble chips by collecting the gas?
e.g. marble chips added to 50 cm³ of dilute hydrochloric acid- Measure the acid into a conical flask, add the marble chips and start the timer.
- Immediately fit a bung with a delivery tube connected to a gas syringe.
- Record the volume of gas every 30 s until it stops rising.
Other than collecting the gas, which measurement shows how much carbon dioxide has been produced in a reaction?
The loss in mass of the flask and contents, found by weighing the flask on a balance. The mass falls as the gas escapes.
In the core practical with sodium thiosulfate and hydrochloric acid, what is timed?
The time taken for a cross drawn under the flask to disappear as the mixture turns cloudy. The shorter the time, the faster the rate.
Why is a gas syringe or a 100 cm³ measuring cylinder better than a 250 cm³ measuring cylinder for measuring the volume of gas produced?
It has smaller gradations / higher resolution, so the volume is measured more precisely.
A student investigates the effect of temperature on the rate of reaction between magnesium ribbon and dilute acid. State three variables that must be kept the same.
Concentration of acid, volume of acid, and the mass and size/surface area of the magnesium.
True or false? Eye protection should be worn throughout a rate experiment using dilute hydrochloric acid.
True. The acid is an irritant and can splash or fizz out of the flask.
Why does increasing the temperature increase the rate of a reaction?
Particles have more energy and move faster, so they collide more frequently, and a higher proportion of collisions have at least the activation energy.
Why does increasing the concentration of a solution increase the rate of a reaction?
There are more particles in the same volume, so there are more frequent collisions.
Why does increasing the pressure of reacting gases increase the rate of a reaction?
The particles are closer together (more particles in the same volume), so collisions are more frequent.
Why does using a solid as a powder instead of large lumps increase the rate of reaction?
The powder has a larger surface area to volume ratio, so there are more frequent collisions and a faster rate.
How can you tell from a graph of gas volume against time that the reaction has finished?
The line levels off / is flat — the volume stays constant.
Why does a graph of gas volume against time become less steep as the reaction goes on?
Reactants are being used up, so there are fewer reacting particles and less frequent collisions.
How is the mean rate of a reaction worked out from the volume of gas produced?
Mean rate = volume of gas produced ÷ time taken, e.g. in cm³ s⁻¹.
The reaction of acid with marble chips is repeated with the same mass of marble and the same volume and concentration of acid, but smaller chips. How does the volume–time curve change?
It is steeper at the start (to the left of the original) and levels off at the same final volume, but sooner.
What is a catalyst?
A substance that speeds up the rate of a reaction without altering the products, and is itself unchanged chemically and in mass at the end.
How does a catalyst increase the rate of a reaction?
It provides an alternative reaction pathway with a lower activation energy.
True or false? Adding a catalyst increases the amount of product made in a reaction.
False. The amount of product is unaltered; the catalyst only makes the reaction faster.
What are the steps to show that a solid catalyst is unchanged in mass at the end of a reaction?
e.g. manganese(IV) oxide added to hydrogen peroxide- Find the mass of the catalyst before the reaction.
- After the reaction, filter off the catalyst and dry it.
- Find the mass of the catalyst again — it is unchanged.
What are enzymes?
Biological catalysts — they speed up reactions in living things.
Enzymes in yeast are used in the production of which type of drink?
Alcoholic drinks (by fermentation).
True or false? Every collision between reactant particles causes a reaction.
False. Only collisions with at least the activation energy are successful and lead to a reaction.
On a graph of the amount of product formed against time, what does a steeper line show?
A faster rate of reaction.
Sodium thiosulfate and hydrochloric acid are both colourless solutions. What makes the mixture turn cloudy when they react?
A yellow precipitate of sulfur forms.
When yeast is used to make alcoholic drinks, what do its enzymes convert sugar (such as glucose) into?
Ethanol and carbon dioxide.