C2.4 - Rates of Reaction Flashcards
What is the “rate of reaction”?
The rate of reaction measures the speed of a reaction or how fast it is.
What is an example of a slow reaction?
A slow reaction may be the rusting of iron.
What is an example of a moderate speed reaction?
A moderate speed reaction may be a metal reacting with an acid.
What is an example of a very fast reaction?
A very fast reaction is an explosion.
What is the rate of reaction dependent on?
Temperature
Concentration of solutions
Pressure in gases
Surface area of solids
Catalyst usage
What denotes a quick reaction on a graph?
The quickest reaction is shown by the line with the steepest slope.
What does it mean if a graph for rate of reaction’s line is high?
If a graph line is higher, then this is because more reactant(s) is added at the start
What is the formula for rate of reaction?
Rate of Reaction = amount of reactant used/product formed/Time
What is a precipitate rate of reaction experiment?
A precipitate rate of reaction experiment is where the product of the reaction is a precipitate that clouds the solution.
How does a precipitate rate of reaction test work?
A precipitate rate of reaction experiment works by observing a mark through the solution and measure how long it takes for it to disappear.
The quicker the mark disappears in a precipitate experiment…
The quicker the mark disappears in a precipitate experiment, the quicker the reaction.
What are the problems with a precipitate rate of reaction experiment?
However, a precipitate rate of reaction experiment only works for reactions where the initial solution is see-through and the result is dependent on when the person looking notes when the mark is no longer visible.
What can a mass balance do?
A mass balance can measure the speed of a reaction that produces a gas.
As the gas is released, the mass disappearing is measured on the balance.
The quicker the reading on the balance drops…
The quicker the reading on the balance drops, the faster the reaction.
What are the positives of a change in mass rate of reaction experiment?
Graphs are easy to plot with this method and the mass balance is very accurate.
What is the negative of a change in mass rate of reaction experiment?
It releases the gas straight into the room.
What is the “volume of gas given off” rate of reaction experiment?
A volume of gas given off rate of reaction experiment is where a gas syringe is used to measure the volume of gas given off.
“The more gas given off in a given time interval…”
The more gas given off in a given time interval, the faster the reaction.
What is a positive and negative of a “volume of gas given off” rate of reaction experiment?
Gas syringes give volumes accurate to the nearest millmitre, hence they are quite accurate, but a too vigorous reaction may lead to the plunger blowing off!
What is the method for a marble chip rate of reaction experiment?
Measure the volume of gas given off with a gas syringe and take readings at regular intervals.
Make a table of readings and plot them as a graph - the time is the x axis and the volume is on the y-axis.
Repeat the experiment with same variables but increase the surface area of the marble chips and subsequently repeat using powdered chalk.
What is the conclusion of the marble chip rate of reaction experiment?
Increasing the mass or surface area increases the rate of reaction as the collisions are more frequent.
What is a magnesium and hydrochloric acid rate of reaction experiment good for?
A magnesium and hydrochloric acid rate of reaction experiment is good for measuring the effects of increased concentration.
How can the product of a magnesium-metal rate of reaction experiment be measured?
The reaction gives off hydrogen gas, which we can measure with a mass balance.
What are the variables for a graph for the magnesium-metal rate of reaction experiment and how would this be done?
Time goes on the x-axis and volume goes on the y-axis.
The readings of mass would be taken at regular time intervals and the results would be put in a table for the loss in mass for each reading, then a graph would be plotted.
What do sodium thiosulfate and HCL have in common? What do they form?
Sodium thiosulfate and HCL are both clear solutions.
They react together to form a yellow sulfur precipitate.
What does a sodium thiosulfate and HCl rate of reaction experiment involve?
The experiment involves watching a black mark disappear through the cloudy sulfur and timing how long this takes to occur.
How is the temperature in a sodium thiosulfate and HCl rate of reaction experiment changed?
The reaction can be repeated at different temperatures by safely using a water bath.
What do the results of a sodium thiosulfate and HCl rate of reaction experiment show?
The results of a sodium thiosulfate and HCl rate of reaction experiment show that the higher the temperature the quicker the reaction and therefore the less time it takes for the mark to disappear.
What is the equation for the decomposition of hydrogen peroxide?
2H2O (aq) + 2H2O (l) + O2(g)
How can the decomposition of hydrogen peroxide be increased?
The decomposition of hydrogen peroxide can be increased with a manganese(IV) oxide catalyst, or potato peels or blood.
What gas is given off in the decomposition of hydrogen peroxide?
Oxygen gas is given off, and this can be used as a means to measure the rate of reaction using a gas syringe.
What is the collision theory?
The collision theory states that reactions can only happen if particles collide, and with enough energy to change into new substances. This is known as activation energy.
What is the effect of increasing temperature on the rate of reaction?
Increasing the temperature increased the kinetic energy of the particles, so the particles collide more frequently. The particles’ increased energy means more of the collisions are of the right activation energy, hence the rate of reaction increases.
What is the effect of increasing pressure on the rate of reaction?
In a gas, increasing the pressure puts more particles into the same volume and reduces the space the particles have to collide in, so there will be more frequent collisions and the rate of reaction increases
What is the effect of increasing concentration on the rate of reaction?
In a solution, increasing the concentration means that there are more reactant particles colliding, making collisions more likely and increasing the rate of reaction.
What is the effect of increasing surface area on the rate of reaction?
Increasing the surface area increases the area that the particles have to work on, so the frequency of collisions will increase. The rate of reaction increases.
What is a catalyst?
A solid catalyst gives the reacting particles a surface to stick to, increasing the number of successful collisions and the rate of reaction.
It is a substance which speeds up a reaction without being changed or used up.
How else do catalysts increase the rate of reaction?
Catalysts may also lower the activation energy, so less energy is needed.
What are the advantages of catalysts?
They increase the rate of reaction, which means the reaction is quicker and requires less energy.
They reduce the activation energy and reduce the energy used up, saving money and fuel.
They are never used up.
They are only required in small amounts.
What are the disadvantages of catalysts?
They are expensive.
They often need to be cleaned.
You need to use a different catalyst for every reaction.
They can be ruined by impurities.
The use of transition metals in catalysts can lead to toxic chemicals being used and environmental damage may occur.
