Rate of Reaction (AQA GCSE Chemistry)
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What is the rate of reaction?
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What is the rate of reaction?
The rate of reaction is a measure of how fast a reactant is used up or how fast a product is made.
Give three techniques used in a lab that are used to measure the rate of a reaction.
Three techniques used in a lab that are used to measure the rate of a reaction include:
measuring mass loss on a balance.
measuring the volume of a gas produced.
measuring a reaction where there is a colour change at the end of the reaction.
State the equation for calculating rate of reaction in terms of reactants.
The equation for calculating rate of reaction in terms of reactants is:
Rate = amount of reactant used / time taken
State the equation for calculating rate of reaction in terms of products.
The equation for calculating rate of reaction in terms of products is:
Rate = amount of product made / time taken
What is the mass loss method?
The mass loss method is a technique for determining reaction rate by measuring the decrease in mass of the reaction vessel, over time, as a gas escapes.
What is the gas collection method?
The gas collection method is a technique for determining reaction rate by measuring the volume of gas produced over time.
What is the precipitation method?
The precipitation method is a technique for determining reaction rate by measuring the time it takes for a precipitate to form and obscure a cross drawn under the reaction vessel.
True or False?
The units for rate of reaction always include time in the denominator.
True.
The units for rate of reaction always include time in the denominator.
Give a disadvantage of measuring the rate of a reaction by collecting gas in an inverted measuring cylinder.
Disadvantages of measuring the rate of a reaction by collecting gas in an inverted measuring cylinder include:
The delivery tube can pop out.
It can be hard to read the scale upside down.
Gas is lost when the bung is connected to the reaction flask.
Give a disadvantage of measuring the rate of a reaction by collecting gas using a gas syringe.
Disadvantages of measuring the rate of a reaction by collecting gas using a gas syringe include:
They are fragile and expensive.
They collect limited volumes.
Gas can be lost while the bung is connected to the flask.
Give an advantage of measuring the rate of a reaction via the formation of a precipitate.
An advantage of measuring the rate of a reaction via the formation of a precipitate is that no specialist equipment is needed.
What are the typical units for expressing rate of reaction in terms of moles?
(Higher tier only)
The typical units for expressing rate of reaction in terms of moles are moles per second, mol/s.
How do you
convert mass per unit time to moles per unit time?
(Higher tier only)
To convert mass per unit time to moles per unit time, divide the mass per unit time by the molar mass of the substance.
What is the molar g
as volume?
(Higher tier only)
The molar gas volume is 24,000 cm3/mol.
How do you convert volume per unit time to moles per unit time for gases?
(Higher tier only)
To convert volume per unit time to moles per unit time for gases, divide the volume per unit time by the molar gas volume (24,000 cm3/mol).
True or False?
There is a direct way to measure moles in a reaction.
(Higher tier only)
False.
There is no direct way to measure moles, so it is necessary to calculate the rate using mass or volume first.
State the equation for converting mass to moles.
(Higher tier only)
The equation for converting mass to moles is:
moles = mass / Mr
What is the first step in calculating rate of reaction in mol/s when given time in minutes?
(Higher tier only)
The first step in calculating rate of reaction in mol/s when given time in minutes is to convert minutes to seconds.
True or False?
The molar gas volume is the same for all gases at room temperature and pressure.
(Higher tier only)
True.
The molar gas volume is the same for all gases at room temperature and pressure.
Which line shows magnesium powder reacting with acid and which line shows magnesium ribbon reacting with acid?
Line A shows magnesium powder reacting with acid and line B shows magnesium ribbon reacting with acid.
How long does the reaction take to complete?
The reactions takes 30 seconds to complete. The point at which the line plateaus is when the reaction is complete.
Which line shows magnesium ribbon reacting with concentrated acid and which line shows magnesium ribbon reacting with dilute acid?
Line A is magnesium reacting with concentrated acid, and line B is magnesium reacting with dilute acid.
At which point is the reaction the fastest?
The reaction is the fastest at the beginning of a reaction. Between 0 and 10 seconds.
True or False?
The gradient of the line in a rates graph is equal to the initial rate of reaction.
True.
The gradient of the line in a rates graph is equal to the initial rate of reaction.
True or False?
The steeper the gradient of the line in a rates graph then the slower the rate of reaction.
False.
The steeper the gradient of the line in a rates graph then the faster the rate of reaction.
What does a horizontal line in a rate graph indicate?
A horizontal line in a rate graph indicates that the reaction has finished.
Which line on the graph indicates a reaction that has taken place at a higher temperature?
The line on the graph that represents the reaction that takes place at a higher temperature is A.
Which line on the graph indicates a reaction that has taken place with a catalyst?
The line on the graph that represents the reaction that takes place with a catalyst is A.
Which lines on the graph indicate a reaction that has taken place between acid and
powdered calcium carbonate?
lumps of calcium carbonate?
The lines on the graph that indicate a reaction that has taken place between acid and
powdered calcium carbonate: A
lumps of calcium carbonate: B
How do you calculate the gradient at a specific point on a curved graph?
(Higher tier only)
To calculate the gradient at a specific point on a curved graph:
Draw a tangent at that point
Determine the change in y
Determine the change in x
The gradient = change in y / change in x.
True or False?
The gradient is constant at all points along a curved rate graph.
(Higher tier only)
False.
The gradient varies at different points along a curved rate graph.
What does the gradient represent in a rate graph?
(Higher tier only)
The gradient represents the rate of reaction at a specific point in time.
True or False?
A steeper tangent indicates a faster rate of reaction at that point.
(Higher tier only)
True.
A steeper tangent indicates a faster rate of reaction at that point.
How can you compare rates of reaction at different points on a curved graph?
(Higher tier only)
You can compare rates of reaction at different points on a curved graph by calculating and comparing the gradients of tangents at those points.
State the equation for calculating gradient.
(Higher tier only)
The equation for calculating gradient is:
gradient = change in y / change in x
What five factors affect the rate of a chemical reaction?
The five factors that can affect the rate of a reaction are:
The concentration of the reactants in solution
The pressure of reacting gases
Surface area of solid reactants
The temperature of the reaction
The presence of a catalyst
What has a greater surface area, magnesium ribbon or magnesium powder?
Magnesium powder has a greater surface area.
How does increasing concentration affect the rate of reaction?
Increasing the concentration will increase the rate of reaction.
True or False?
Adding a catalyst to a reaction will decrease the rate.
False.
Adding a catalyst to a reaction will increase the rate.
How does decreasing temperature affect the rate of reaction?
Decreasing temperature decreases the rate of reaction.
True or False?
It is of economic interest to have a higher rate of reaction as this implies a higher rate of production and hence a more efficient and sustainable process.
True.
It is of economic interest to have a higher rate of reaction as this implies a higher rate of production and hence a more efficient and sustainable process.
How does increasing surface area affect the rate of reaction?
Increasing surface area increases the rate of reaction.
How does the time for a reaction to complete change when temperature is increased?
The time for a reaction to complete decreases when temperature is increased.
True or False?
Decreasing particle size has the same effect as increasing surface area.
True.
Decreasing particle size has the same effect as increasing surface area.
What happens to the amount of product formed when a catalyst is added?
The amount of product formed remains the same when a catalyst is added, but it forms more quickly.
Define the term collision theory.
Collision theory explains how rates of reaction depend on the frequency and energy of collisions between reactant particles.
Define the term activation energy.
The minimum energy required for reactant particles to undergo a chemical reaction.
True or False?
Increasing concentration increases the number of collisions per second.
True.
Increasing the concentration of a solution will increase the number of reactant particles in a given volume, allowing more frequent and successful collisions per second.
How does increasing temperature increase the rate of reaction?
Increasing temperature:
Increases the kinetic energy of the particles,
Leading to more frequent and successful collisions with energy greater than the activation energy.
How does increasing surface area affect the rate of reaction?
Increasing the surface area of a solid reactant increases the rate of reaction because more particles are exposed to the other reactant, producing a higher number of collisions per second.
State the relationship between the number of collisions and the number of particles.
The number of collisions is proportional to the number of particles present.
Define the term successful collision.
A successful collision is a collision between reactant particles that leads to the formation of product molecules.
What is the symbol for activation energy?
The symbol for activation energy is Ea.
True or False?
All collisions result in a chemical reaction.
False.
Not all collisions result in a chemical reaction.
Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds.
Define the term catalyst.
A catalyst is a substance that increases the rate of a reaction without being used up itself.
How does a catalyst work?
A catalyst speeds up the rate of a reaction by providing an alternative pathway with lower activation energy.
True or False?
Catalysts are used up in a reaction.
False.
Catalysts are not used up in the reaction.
True or False?
Catalysts are written as part of the chemical equation.
False.
Although catalysts are not part of the overall reaction, they may be written over the arrow in reaction equations, indicating the conditions.
True or False?
Only small amounts of a catalyst are needed in a reaction.
True.
Only small amounts of a catalyst are needed in a reaction as the catalyst is not used up.
How can you show that a chemical is a catalyst?
You can show that a substance is a catalyst by:
Weigh the catalyst before the reaction
Weigh the catalyst after the reaction
The mass should remain the same
Which letter represents the activation energy for a reaction using a catalyst?
The letter which represents the activation energy for a reaction using a catalyst is C.
True or False?
Enzymes are biological catalysts.
True.
Enzymes are nature's catalysts, biological substances that catalyse reactions in living cells.
