Rates of reaction

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课程笔记

What is Rate of Reaction?

Rate of reaction is how quickly a chemical reaction takes place.
It depends on the frequency of successful collisions between reacting particles.
A successful collision has enough energy and correct orientation to react.

Factors Affecting Rate of Reaction

Temperature: Higher temperature → particles move faster → more frequent and energetic collisions → faster rate.
Concentration/Pressure: Higher concentration or pressure → more particles in same volume → more collisions → faster rate.
Surface Area: Breaking solid into smaller pieces increases surface area to volume ratio → more collisions on surface → faster rate.
Catalyst: A substance that increases rate without being used up; provides an alternative pathway with lower activation energy.

Measuring Rate of Reaction

Change in mass: For reactions producing a gas, measure mass loss over time (e.g., magnesium + hydrochloric acid → hydrogen gas escapes).
Volume of gas: Collect gas in a gas syringe and measure volume produced over time.
Precipitation: Time how long for a precipitate to form (e.g., sodium thiosulfate + HCl → yellow sulfur; use a black cross to observe cloudiness).
Colour change: Time how long for a colour change to occur.

Example: Magnesium and Hydrochloric Acid

Reaction: Mg + 2HCl → MgCl₂ + H₂ (hydrogen gas produced).
Rate can be measured by mass loss (escaping hydrogen) or gas volume in a syringe.
Using magnesium powder (higher surface area) gives a faster rate than large pieces.

Example: Sodium Thiosulfate and Hydrochloric Acid

Reaction: Na₂S₂O₃ + 2HCl → 2NaCl + SO₂ + S + H₂O (yellow sulfur precipitate).
Place flask over a black cross; time until cross is no longer visible due to cloudiness.
Increasing concentration or temperature of HCl increases rate (faster precipitation).

Particle arrangement in solids, liquids, and gases. In solids, particles are closely packed in a regular pattern; in liquids, they are close but irregular; in gases, they are far apart and move randomly. Higher temperature increases particle speed and collision frequency.

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练习题

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1.What is meant by the term 'rate of reaction'?
Easy
- AHow quickly a chemical reaction takes place
- BThe amount of product formed in a reaction
- CThe temperature at which a reaction occurs
- DThe energy released during a reaction
2.Which of the following statements is true?
Medium
- AParticles at a higher temperature move more quickly.
- BA catalyst is used up during a chemical reaction.
- CBreaking a solid into smaller pieces decreases its surface area to volume ratio.
- DThe rate of reaction does not depend on the frequency of successful collisions.
3.What is a catalyst?
Easy
- AA substance that increases the rate of reaction without being used up
- BA substance that slows down a reaction
- CA substance that is consumed in a reaction
- DA substance that increases the activation energy
4.Which of the following methods can be used to measure the rate of a reaction that produces a gas?
Medium
- AMeasuring the change in mass
- BObserving a colour change
- CUsing a light sensor to detect precipitate formation
- DTiming the appearance of a precipitate
5.In the reaction between sodium thiosulfate and hydrochloric acid, what is observed as the reaction proceeds?
Easy
- AA yellow sulfur precipitate forms, making the solution cloudy
- BA colourless gas is produced
- CThe solution turns blue
- DThe mass of the reaction mixture increases
6.Increasing the concentration of a reactant increases the rate of reaction because:
Medium
- AThere are more particles in the same volume, leading to more frequent collisions
- BThe particles move faster
- CThe activation energy is lowered
- DThe particles have more energy
7.Which of the following would increase the rate of reaction between magnesium and hydrochloric acid?
Medium
- AUsing magnesium powder instead of large pieces
- BDecreasing the temperature
- CUsing a more dilute hydrochloric acid
- DUsing a larger volume of the same concentration of acid
8.In an experiment to measure the rate of reaction between magnesium and hydrochloric acid, which method would be most appropriate?
Medium
- AMeasuring the volume of hydrogen gas produced over time using a gas syringe
- BObserving the colour change of the solution
- CUsing a light sensor to detect precipitate formation
- DMeasuring the increase in mass of the reaction mixture

更多题目

9.A catalyst increases the rate of reaction by:
Medium
- AProviding an alternative pathway with a lower activation energy
- BIncreasing the temperature of the reactants
- CIncreasing the concentration of the reactants
- DIncreasing the surface area of the reactants
10.Which of the following statements about pressure and rate of reaction is correct?
Medium
- AA gas at higher pressure has more particles in the same volume, increasing the rate of reaction
- BA gas at higher pressure has fewer particles in the same volume, decreasing the rate of reaction
- CPressure has no effect on the rate of reaction
- DIncreasing pressure decreases the frequency of collisions
11.In the reaction between sodium thiosulfate and hydrochloric acid, the rate can be measured by:
Easy
- ATiming how long it takes for a black cross under the flask to become invisible
- BMeasuring the volume of gas produced
- CMeasuring the change in mass
- DMonitoring the temperature change
12.Which factor does NOT affect the rate of a chemical reaction?
Easy
- AThe colour of the reactants
- BTemperature
- CConcentration
- DSurface area
13.In the reaction between magnesium and hydrochloric acid, the mass of the reaction mixture decreases over time because:
Medium
- AHydrogen gas escapes from the flask
- BMagnesium dissolves completely
- CThe acid evaporates
- DWater is produced and evaporates
14.A student investigates the reaction between sodium thiosulfate and hydrochloric acid. They measure the time for a black cross to disappear. Which change would increase the rate of reaction?
Medium
- AUsing a more dilute solution of sodium thiosulfate
- BCooling the hydrochloric acid to 10°C
- CAdding a catalyst that lowers activation energy
- DUsing a smaller conical flask
15.In an experiment, 0.5 g of magnesium ribbon reacts with excess hydrochloric acid. The volume of hydrogen gas produced is measured every 10 seconds. After 60 seconds, 40 cm³ of gas has been collected. What is the average rate of reaction in cm³ per second?
Medium
- A0.67 cm³/s
- B0.83 cm³/s
- C1.5 cm³/s
- D2.4 cm³/s
16.A student uses a gas syringe to collect carbon dioxide from the reaction of calcium carbonate with hydrochloric acid. They record the volume of gas at 20-second intervals. Which graph shape would show a decreasing rate over time?
Medium
- AA straight line through the origin
- BA curve that becomes less steep over time
- CA curve that becomes steeper over time
- DA horizontal line
17.Which of the following units could be used to measure the rate of a reaction that produces a gas?
Easy
- Ag/s
- Bcm³/s
- Cboth g/s and cm³/s
- Dmol/dm³
18.In an experiment, marble chips (calcium carbonate) react with hydrochloric acid. The mass of the flask and contents is measured every minute. After 2 minutes, the mass has decreased by 0.6 g. What mass of carbon dioxide has been produced?
Medium
- A0.3 g
- B0.6 g
- C1.2 g
- D0.0 g
19.To measure the rate of a reaction that forms a precipitate, a student could use:
Easy
- AA gas syringe
- BA balance
- CA light sensor
- DA thermometer
20.A student adds 2 g of magnesium powder to 50 cm³ of hydrochloric acid. The same mass of magnesium ribbon is added to another 50 cm³ of the same acid. Which statement is correct?
Medium
- AThe powder reacts faster because it has a larger surface area
- BThe ribbon reacts faster because it is denser
- CBoth react at the same rate because the mass is equal
- DThe powder reacts slower because it sinks
21.A reaction between two gases is carried out in a sealed container. The volume of the container is halved. What effect does this have on the rate of reaction?
Medium
- AThe rate increases because pressure increases
- BThe rate decreases because volume decreases
- CThe rate stays the same because the number of particles is unchanged
- DThe rate increases because temperature rises
22.Which of the following is a catalyst?
Easy
- AAn enzyme
- BA reactant
- CA product
- DA solvent
23.A student investigates the effect of temperature on the reaction between sodium thiosulfate and hydrochloric acid. They measure the time for a cross to disappear. Which variable should they keep constant?
Medium
- ATemperature of the acid
- BConcentration of sodium thiosulfate
- CVolume of hydrochloric acid
- DBoth concentration of sodium thiosulfate and volume of hydrochloric acid
24.The graph shows the volume of gas produced over time for two experiments: one at 20°C and one at 30°C. The initial rate is higher at 30°C. After 5 minutes, the total volume of gas is the same for both. This is because:
Hard
- AThe reaction at 30°C finishes earlier but both produce the same amount of product
- BThe reaction at 30°C produces more gas overall
- CThe reaction at 20°C has a higher activation energy
- DThe catalyst works better at 30°C
25.Which of the following statements about particles at higher temperature is correct?
Easy
- AThey move more quickly.
- BThey move more slowly.
- CThey have the same speed as at lower temperature.
- DThey stop moving.
26.A catalyst increases the rate of a chemical reaction by:
Easy
- Aproviding an alternative pathway with lower activation energy
- Bbeing used up in the reaction
- Cincreasing the temperature of the reactants
- Dincreasing the concentration of the reactants
27.In the reaction between sodium thiosulfate and hydrochloric acid, a yellow precipitate of sulfur is formed. Which method would be most suitable for measuring the rate of this reaction?
Medium
- AMeasuring the volume of gas produced
- BMeasuring the change in mass
- CObserving the time for a black cross to become invisible
- DUsing a pH meter
28.A student investigates the effect of surface area on the rate of reaction between magnesium and hydrochloric acid. They use 0.5 g of magnesium ribbon and 0.5 g of magnesium powder separately with excess acid. Which experimental setup would allow them to compare the rates most accurately?
Medium
- AMeasure the volume of hydrogen gas produced every 10 seconds using a gas syringe
- BMeasure the temperature change of the solution after 2 minutes
- CObserve the colour change of the solution
- DWeigh the flask before and after the reaction
29.Which of the following would increase the rate of reaction between a gas and a solid?
Easy
- ADecreasing the pressure of the gas
- BUsing larger pieces of solid
- CIncreasing the concentration of the gas
- DDecreasing the temperature
30.In an experiment to measure the effect of temperature on the reaction between sodium thiosulfate and hydrochloric acid, which variable should be kept constant?
Medium
- AThe temperature of the acid
- BThe concentration of sodium thiosulfate
- CThe time for the cross to disappear
- DThe volume of sulfur precipitate
31.Which of the following is a correct method to measure the rate of a reaction that produces a gas?
Easy
- AMeasure the increase in mass of the reaction mixture
- BMeasure the volume of gas produced using a gas syringe
- CMeasure the time for a colour change to occur
- DMeasure the change in pH of the solution
32.A student adds 2 g of magnesium ribbon to 50 cm³ of hydrochloric acid at 20°C. In a second experiment, they use the same mass of magnesium powder with 50 cm³ of the same acid at 20°C. Which statement is correct?
Medium
- AThe powder will react faster because it has a larger surface area.
- BThe ribbon will react faster because it has a larger surface area.
- CBoth will react at the same rate because the mass is the same.
- DThe powder will react faster because it has a higher concentration.
33.A reaction between two gases takes place in a sealed container. The pressure inside the container is doubled by adding more gas. What effect does this have on the rate of reaction?
Medium
- AThe rate increases because there are more particles in the same volume.
- BThe rate decreases because the particles are closer together.
- CThe rate stays the same because the temperature is constant.
- DThe rate increases because the particles move faster.
34.A student investigates the effect of a catalyst on the decomposition of hydrogen peroxide. They measure the volume of oxygen gas produced over time. Which of the following would indicate that a catalyst is present?
Medium
- AThe total volume of oxygen produced is greater with the catalyst.
- BThe initial rate of gas production is faster with the catalyst.
- CThe catalyst changes colour during the reaction.
- DThe catalyst is consumed and must be added continuously.
35.Which of the following statements about particles at a higher temperature is correct?
Easy
- AThey move more quickly.
- BThey move more slowly.
- CThey have the same speed as at lower temperature.
- DThey stop moving.
36.A catalyst is a substance that increases the rate of reaction. Which of the following is true about a catalyst?
Easy
- AIt is used up during the reaction.
- BIt provides an alternative pathway with lower activation energy.
- CIt increases the temperature of the reaction.
- DIt decreases the concentration of reactants.
37.The rate of reaction depends on the frequency of successful collisions between reacting particles. Which factor does NOT affect the rate of reaction?
Medium
- ATemperature
- BConcentration
- CColour of reactants
- DSurface area
38.Breaking a solid into smaller pieces increases its rate of reaction because:
Easy
- AIt decreases the surface area to volume ratio.
- BIt increases the surface area to volume ratio.
- CIt increases the mass of the solid.
- DIt changes the chemical composition.
39.Which of the following statements about gas pressure and rate of reaction is correct?
Medium
- AHigher pressure decreases the number of particles per volume.
- BHigher pressure increases the rate of reaction because particles are closer together.
- CHigher pressure has no effect on reaction rate.
- DHigher pressure slows down particles.
40.In the reaction between sodium thiosulfate and hydrochloric acid, a yellow precipitate of sulfur forms. Which method is most suitable for measuring the rate of this reaction?
Medium
- AMeasuring the volume of gas produced
- BMeasuring the change in mass
- CObserving the time for a black cross to disappear
- DUsing a pH meter
41.Particles at a higher temperature move more quickly.
Easy
True or false?
42.A catalyst is used up during a chemical reaction.
Easy
True or false?
43.The rate of reaction depends on the frequency of successful collisions.
Easy
True or false?
44.Breaking a solid up into smaller pieces decreases the surface area to volume ratio.
Easy
True or false?
45.A gas at a higher pressure has more particles in the same volume.
Easy
True or false?
46.In the reaction between sodium thiosulfate and hydrochloric acid, a yellow sulfur precipitate is formed. Which method is most suitable for measuring the rate of this reaction?
Medium
- AMeasuring the change in mass of the reaction mixture
- BCollecting the gas produced in a gas syringe
- CTiming how long it takes for a black cross to disappear when viewed through the solution
- DUsing a pH meter to measure the change in acidity
47.Magnesium is added to hydrochloric acid. Which form of magnesium would have a higher rate of reaction?
Easy
- ALarge pieces of magnesium
- BMagnesium powder
- CBoth have the same rate
- DNeither reacts
48.Which of the following correctly describes how a catalyst increases the rate of reaction?
Easy
- AIt is used up in the reaction, providing extra energy.
- BIt provides an alternative pathway with a lower activation energy.
- CIt increases the temperature of the reactants.
- DIt increases the concentration of reactants.
49.A student reacts magnesium with hydrochloric acid and measures the mass loss over time. Which of the following would cause the fastest initial rate?
Medium
- ALarge magnesium ribbon at 20°C
- BMagnesium powder at 20°C
- CLarge magnesium ribbon at 30°C
- DMagnesium powder at 30°C
50.Match each factor affecting rate of reaction to its correct explanation.
Hard
- Increasing temperature
- Increasing concentration
- Increasing surface area
- Adding a catalyst
- Provides alternative pathway with lower activation energy
- Particles move faster and collide more energetically
- More particles in same volume leads to more collisions
- More surface exposed for collisions
51.Explain why increasing the temperature of reactants increases the rate of reaction.
Medium
52.State what effect increasing the concentration of hydrochloric acid would have on the reaction between sodium thiosulfate and hydrochloric acid. Explain the reasons why.
Medium
53.Describe an experiment that could investigate how the rate of reaction depends on the temperature of hydrochloric acid when reacting with sodium thiosulfate.
Hard
54.Complete the sentences about factors affecting rate of reaction.
Easy
Breaking a solid into smaller pieces increases its ____ to volume ratio, which increases the rate of reaction. A gas at higher ____ has more particles in the same volume.

复习笔记

## Rates of Reaction - **Rate of reaction** = how quickly a chemical reaction takes place. - Depends on **frequency of successful collisions** between reacting particles. ### Factors Affecting Rate - **Temperature**: Higher temperature → particles move faster → more frequent and energetic collisions → faster rate. - **Concentration/Pressure**: Higher concentration (solution) or higher pressure (gas) → more particles in same volume → more collisions → faster rate. - **Surface Area**: Smaller solid pieces (e.g., powder) → larger surface area to volume ratio → more collisions on surface → faster rate. - **Catalyst**: Substance that increases rate without being used up. Provides alternative pathway with **lower activation energy**. ### Measuring Rate - **Change in mass**: For reactions producing gas (e.g., Mg + HCl → MgCl₂ + H₂). Mass decreases as gas escapes. - **Volume of gas**: Collect gas in a gas syringe and measure volume over time. - **Precipitation**: Time for precipitate to form (e.g., sodium thiosulfate + HCl → yellow sulfur). Use a black cross under flask; time until cross is no longer visible. - **Colour change**: Time for colour change to occur. ### Key Points - True/False: (a) True, (b) False, (c) True, (d) False, (e) True. - Increasing temperature increases particle speed and collision energy. - Increasing concentration increases particle number and collision frequency. - Powder has higher rate than large pieces due to larger surface area. - Experiment: Use balance to measure mass loss over time for Mg + HCl.

Rate of reaction: How quickly a chemical reaction takes place.
Successful collisions: Collisions between reacting particles that result in a reaction.
Catalyst: A substance that increases the rate of reaction without being used up.
Activation energy: The minimum energy needed for a collision to result in a reaction.
Precipitate: A solid formed in a solution during a chemical reaction.

闪卡

What does the phrase 'rate of reaction' mean?

It means how quickly a chemical reaction takes place.

What does the rate of reaction depend on?

It depends on the frequency of successful collisions between reacting particles.

How does temperature affect the rate of reaction?

Higher temperatures cause particles to move more quickly, increasing the frequency and energy of collisions, thus increasing the rate of reaction.

How does concentration affect the rate of reaction?

In a more concentrated solution, there are more particles in the same volume, leading to a higher rate of collisions and increasing the rate of reaction.

How does pressure affect the rate of reaction for gases?

A gas at higher pressure has more particles in the same volume, leading to a higher rate of collisions and increasing the rate of reaction.

How does surface area affect the rate of reaction?

Breaking a solid into smaller pieces increases its surface area to volume ratio, allowing more collisions on the surface and increasing the rate of reaction.

What is a catalyst?

A catalyst is a substance that increases the rate of reaction without being used up in the process.

How does a catalyst increase the rate of reaction?

It provides an alternative pathway with a lower activation energy, increasing the rate at which collisions result in a reaction.

Name one method to measure the rate of reaction that produces a gas.

Measuring the change in mass (loss of mass) as gas escapes.

Give an example of a reaction where measuring change in mass is used to find the rate.

The reaction between magnesium and hydrochloric acid to form magnesium chloride and hydrogen gas.

How can the volume of gas produced be used to measure rate of reaction?

Capture the gas in a gas syringe and measure the volume of gas produced over time.

What is precipitation in the context of rate of reaction?

Precipitation is the formation of a solid in a solution during a chemical reaction.

How can precipitation be used to measure rate of reaction?

By observing the time it takes for the precipitate to form, either visually or using a light sensor to detect cloudiness.

Give an example of a reaction where precipitation is used to measure rate.

The reaction between sodium thiosulfate and hydrochloric acid, which forms a yellow sulfur precipitate.

Describe the experiment using sodium thiosulfate and hydrochloric acid to measure rate.

Place the reaction mixture in a conical flask above a piece of paper with a black cross. Measure the time for the black cross to no longer be visible due to the precipitate.

How can colour change be used to measure rate of reaction?

Time how long it takes for the colour change to occur.

True or false: Particles at a higher temperature move more quickly.

True.

True or false: A catalyst is used up during a chemical reaction.

False.

True or false: The rate of reaction depends on the frequency of successful collisions.

True.

True or false: Breaking a solid up into smaller pieces decreases the surface area to volume ratio.

False.

True or false: A gas at a higher pressure has more particles in the same volume.

True.

Explain why increasing the temperature of reactants increases the rate of reaction.

Higher temperatures cause particles to move more quickly, increasing the frequency and energy of collisions, so more collisions are successful.

What effect does increasing the concentration of hydrochloric acid have on the reaction with sodium thiosulfate?

It increases the rate of reaction because there are more particles in the same volume, leading to a higher frequency of collisions.

Describe an experiment to investigate how the rate of reaction depends on the temperature of hydrochloric acid using sodium thiosulfate.

Use a conical flask above a black cross. Add sodium thiosulfate and hydrochloric acid at different temperatures. Measure the time for the cross to disappear. Repeat at several temperatures.

Which has a higher rate of reaction: magnesium powder or large pieces of magnesium with hydrochloric acid?

Magnesium powder has a higher rate because it has a larger surface area to volume ratio, allowing more collisions on the surface.

Describe how to experimentally verify which form of magnesium (powder or large pieces) has a higher rate of reaction with hydrochloric acid.

Use a balance to measure mass loss over time. Add the same mass of magnesium powder and large pieces separately to excess hydrochloric acid. The faster mass loss indicates a higher rate.

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