Define rate of reaction .

A rate of reaction is a measure of the speed of a chemical reaction. It is found by tracking how a quantity (mass or volume) changes over a period of time.

True or False? A cotton wool plug is used in a mass loss experiment to stop gas escaping from the flask.

False. A cotton wool plug lets the gas out but stops acid from splashing out of the flask, which would give an incorrect mass reading.

Why does a reaction rate graph curve flatten out as a horizontal line?

The curve flattens because at least one reactant has been completely used up . With no reactants left, collisions stop and the reaction ends. The rate becomes zero.

To monitor a rate of reaction, you track how a .......... (such as mass or volume) changes over a set period of .......... .

To monitor a rate of reaction, you track how a quantity (such as mass or volume) changes over a set period of time .

Name the three methods used in the lab to monitor a rate of reaction.

Mass loss — measuring the decrease in mass as a gas escapes from the flask Gas collection — recording gas volume using a gas syringe or collecting over water Disappearing cross — timing how long a precipitate takes to hide a cross underneath the flask

True or False? Two reactions at different temperatures always produce different amounts of product.

False. Temperature only affects the rate , not the total amount of product. Both curves finish at the same height on a rate graph.

What is the disappearing cross experiment ?

A disappearing cross experiment is a method used to monitor the rate of a reaction that forms a precipitate . A flask is placed over a black cross and the time is recorded for the mixture to become cloudy enough to hide the cross.

Why does a faster reaction produce a steeper curve on a rate of reaction graph?

A faster reaction produces a steeper curve because reactant particles are colliding more frequently per second . More product is formed each second, so the volume or mass increases more quickly at the start.

If you halve the concentration of a reactant, the curve on a rate graph will be .......... steep and reach a .......... final volume compared to the original.

If you halve the concentration of a reactant, the curve on a rate graph will be less steep and reach a lower final volume compared to the original.

Name the four factors that can increase the rate of a chemical reaction.

Increasing temperature Increasing concentration of a reactant Increasing surface area / decreasing particle size Using a catalyst

True or False? A catalyst is used up during a chemical reaction.

False. A catalyst speeds up a reaction but is not used up . It can be recovered chemically unchanged at the end of the reaction.

A catalyst is a substance that increases the rate of a chemical reaction without being used up. It works by providing an alternative reaction pathway , which increases the number of successful collisions per second.

Why does increasing temperature increase the rate of a chemical reaction?

At higher temperatures, reactant particles have more kinetic energy and move faster. This causes collisions to be more frequent and more energetic , so a higher proportion of collisions are successful.

Increasing the concentration of a reactant increases the rate because there are more particles per .......... , leading to more .......... collisions.

Increasing the concentration of a reactant increases the rate because there are more particles per unit volume , leading to more frequent collisions.

True or False? A reaction carried out at a higher temperature produces more product than the same reaction at a lower temperature.

False. Temperature only affects the rate . The total amount of product depends on the amount of reactant, not the temperature. The curves finish at the same height on a rate graph.

Why does breaking a solid reactant into smaller pieces increase the rate of reaction?

Breaking a solid into smaller pieces increases the surface area . This exposes more reactant particles at the surface, leading to more frequent collisions and more successful collisions per second.

All four factors that increase the rate of reaction (temperature, concentration, surface area and catalyst) work by increasing the number of .......... per second.

All four factors that increase the rate of reaction (temperature, concentration, surface area and catalyst) work by increasing the number of successful collisions per second.

What catalyst is used in the Haber process, and what does it produce?

The Haber process uses an iron catalyst to make ammonia . The catalyst is not used up and allows the reaction to occur faster, saving energy costs in industry.

Define average rate of reaction .

An average rate of reaction measures the change in quantity of a reactant or product over a specific time period. It is calculated using: average rate = Δquantity ÷ Δt, where Δ means "change in."

Δquantity is calculated by subtracting the .......... quantity from the .......... quantity.

Δquantity is calculated by subtracting the initial quantity from the final quantity.

Why is the rate of reaction fastest at the very start of a reaction?

At the start, the concentration of reactants is highest . This means collisions between particles are most frequent, so the number of successful collisions per second is at its greatest.

True or False? The rate of reaction stays constant throughout the reaction.

False. The rate changes as the reaction progresses. It is fastest at the start and slows down as reactants are used up, eventually reaching zero.

A reaction produces 15 cm 3 of gas in the first 20 seconds. Calculate the average rate in cm 3 s -1 .

An average rate is calculated using average rate = Δquantity ÷ Δt. average rate = 15 ÷ 20 average rate = 0.75 cm 3 s -1

True or False? At the end of a reaction, the rate falls to zero.

True. When at least one reactant is completely used up , there are no more particles to collide. The reaction stops and the rate becomes zero.

A student measures mass in grams and time in seconds during a reaction. State the units of the average rate.

The units of average rate are found by putting the quantity unit "per" the time unit. If mass is in g and time in s , the unit of average rate is g s -1 .

To find the time taken for a reaction, rearrange the average rate formula: Δt = Δquantity ÷ .......... .

To find the time taken for a reaction, rearrange the average rate formula: Δt = Δquantity ÷ average rate .

Why does the rate of reaction decrease as the reaction progresses?

As the reaction progresses, reactants are used up . Their concentration falls, so collisions between particles become less frequent and the rate decreases.

National 5ChemistrySQAFlashcardsChemical Changes & StructureRates of Reaction

Rates of Reaction (SQA National 5 Chemistry): Flashcards

Exam code: X813 75

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Cards in this collection (27)

Define rate of reaction.
A rate of reaction is a measure of the speed of a chemical reaction. It is found by tracking how a quantity (mass or volume) changes over a period of time.
True or False?
A cotton wool plug is used in a mass loss experiment to stop gas escaping from the flask.
False.
A cotton wool plug lets the gas out but stops acid from splashing out of the flask, which would give an incorrect mass reading.
Why does a reaction rate graph curve flatten out as a horizontal line?
The curve flattens because at least one reactant has been completely used up. With no reactants left, collisions stop and the reaction ends. The rate becomes zero.
To monitor a rate of reaction, you track how a .......... (such as mass or volume) changes over a set period of ...........
To monitor a rate of reaction, you track how a quantity (such as mass or volume) changes over a set period of time.
Name the three methods used in the lab to monitor a rate of reaction.
1. Mass loss — measuring the decrease in mass as a gas escapes from the flask
2. Gas collection — recording gas volume using a gas syringe or collecting over water
3. Disappearing cross — timing how long a precipitate takes to hide a cross underneath the flask
True or False?
Two reactions at different temperatures always produce different amounts of product.
False.
Temperature only affects the rate, not the total amount of product. Both curves finish at the same height on a rate graph.
What is the disappearing cross experiment?
A disappearing cross experiment is a method used to monitor the rate of a reaction that forms a precipitate. A flask is placed over a black cross and the time is recorded for the mixture to become cloudy enough to hide the cross.
Why does a faster reaction produce a steeper curve on a rate of reaction graph?
A faster reaction produces a steeper curve because reactant particles are colliding more frequently per second. More product is formed each second, so the volume or mass increases more quickly at the start.
If you halve the concentration of a reactant, the curve on a rate graph will be .......... steep and reach a .......... final volume compared to the original.
If you halve the concentration of a reactant, the curve on a rate graph will be less steep and reach a lower final volume compared to the original.
Name the four factors that can increase the rate of a chemical reaction.
1. Increasing temperature
2. Increasing concentration of a reactant
3. Increasing surface area / decreasing particle size
4. Using a catalyst
True or False?
A catalyst is used up during a chemical reaction.
False.
A catalyst speeds up a reaction but is not used up. It can be recovered chemically unchanged at the end of the reaction.
Define catalyst.
A catalyst is a substance that increases the rate of a chemical reaction without being used up. It works by providing an alternative reaction pathway, which increases the number of successful collisions per second.
Why does increasing temperature increase the rate of a chemical reaction?
At higher temperatures, reactant particles have more kinetic energy and move faster. This causes collisions to be more frequent and more energetic, so a higher proportion of collisions are successful.
Increasing the concentration of a reactant increases the rate because there are more particles per .........., leading to more .......... collisions.
Increasing the concentration of a reactant increases the rate because there are more particles per unit volume, leading to more frequent collisions.
True or False?
A reaction carried out at a higher temperature produces more product than the same reaction at a lower temperature.
False.
Temperature only affects the rate. The total amount of product depends on the amount of reactant, not the temperature. The curves finish at the same height on a rate graph.
Why does breaking a solid reactant into smaller pieces increase the rate of reaction?
Breaking a solid into smaller pieces increases the surface area. This exposes more reactant particles at the surface, leading to more frequent collisions and more successful collisions per second.
All four factors that increase the rate of reaction (temperature, concentration, surface area and catalyst) work by increasing the number of .......... per second.
All four factors that increase the rate of reaction (temperature, concentration, surface area and catalyst) work by increasing the number of successful collisions per second.
What catalyst is used in the Haber process, and what does it produce?
The Haber process uses an iron catalyst to make ammonia. The catalyst is not used up and allows the reaction to occur faster, saving energy costs in industry.
Define average rate of reaction.
An average rate of reaction measures the change in quantity of a reactant or product over a specific time period. It is calculated using: average rate = Δquantity ÷ Δt, where Δ means "change in."
Δquantity is calculated by subtracting the .......... quantity from the .......... quantity.
Δquantity is calculated by subtracting the initial quantity from the final quantity.
Why is the rate of reaction fastest at the very start of a reaction?
At the start, the concentration of reactants is highest. This means collisions between particles are most frequent, so the number of successful collisions per second is at its greatest.
True or False?
The rate of reaction stays constant throughout the reaction.
False.
The rate changes as the reaction progresses. It is fastest at the start and slows down as reactants are used up, eventually reaching zero.
A reaction produces 15 cm³ of gas in the first 20 seconds. Calculate the average rate in cm³ s^-1.
An average rate is calculated using average rate = Δquantity ÷ Δt.
average rate = 15 ÷ 20
average rate = 0.75 cm³ s^-1
True or False?
At the end of a reaction, the rate falls to zero.
True.
When at least one reactant is completely used up, there are no more particles to collide. The reaction stops and the rate becomes zero.
A student measures mass in grams and time in seconds during a reaction. State the units of the average rate.
The units of average rate are found by putting the quantity unit "per" the time unit. If mass is in g and time in s, the unit of average rate is g s^-1.
To find the time taken for a reaction, rearrange the average rate formula: Δt = Δquantity ÷ .......... .
To find the time taken for a reaction, rearrange the average rate formula: Δt = Δquantity ÷ average rate.
Why does the rate of reaction decrease as the reaction progresses?
As the reaction progresses, reactants are used up. Their concentration falls, so collisions between particles become less frequent and the rate decreases.

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