Unit B Lesson 14: The Rate of a Chemical Reaction
Completion requirements
Unit B Lesson 14: The Rate of a Chemical Reaction
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Learning Targets |
Big Question: How can I influence the rate of a chemical reaction?
Let's review the many ways to name and rite formulas for chemical compounds.
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Let's review the many ways to name and rite formulas for chemical compounds.
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At the end of this inquiry, you should be able to answer the following questions:
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What are four factors that affect the rate of chemical reactions?
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Is a catalyst consumed in a chemical reaction?
- What is the difference between a catalyst and an enzyme?
- How is the rate of a chemical reaction affected by
- the concentration of a solution
- a catalyst
- surface area
- temperature
Pages 166 and 169 in your textbook will help you answer these questions about the rate of a chemical reaction.
Periodic Table links:
Introduction
Energy in the form of heat is required to cook food.
The energy may come from boiling water or the burner on the stove, a microwave or conventional oven. Whatever the case, the warmer the temperature, the faster food cooks.
The energy may come from boiling water or the burner on the stove, a microwave or conventional oven. Whatever the case, the warmer the temperature, the faster food cooks.
On the, other hand, to preserve food, a refrigerator is used.
The cool temperature in the refrigerator helps to slow the spoiling process. The warmer the temperature, the faster food spoils.
The cool temperature in the refrigerator helps to slow the spoiling process. The warmer the temperature, the faster food spoils.
Temperature has an effect on the rate at which food cooks and on the rate at which it spoils. When food is cooked or when it spoils, many chemical reactions occur. Therefore, temperature has an effect on how fast chemical reactions occur.
In this section, you will learn about the four factors that influence the rate of a chemical reaction.
In this section, you will learn about the four factors that influence the rate of a chemical reaction.
- Having a catalyst to speed up the chemical reaction.
- Having a higher concentration of reactants to speed up the reaction, or lower concentrations to slow the reaction down.
- Having a higher temperature to speed up the reaction, or lower temperatures to slow the reaction down.
- Having more surface area of the reactants to speed up the reaction, or less surface area to slow the reaction down.
Watch
Watch the following video for an excellent overview of factors that affect chemical reaction rate.
Catalysts and the Rate of Chemical Reactions
How does a catalyst affect the rate of reaction? Let us look at the example of adding zinc to iodine. Click on the video below to watch how zinc reacts with iodine.
How does a catalyst affect the rate of reaction? Let us look at the example of adding zinc to iodine. Click on the video below to watch how zinc reacts with iodine.
A exothermic reaction occurs between zinc and iodine to produce zinc iodide according to the equation:
zinc + iodine → zinc iodide + heat
zinc + iodine → zinc iodide + heat
Here is exactly what occurs when you add powdered zinc to powdered iodine:
Why is the water necessary for this reaction to proceed? Water is a catalyst in this reaction. Catalysts are substances that help a reaction proceed faster. They are mixed with the reactants but are not consumed in a reaction. Water allows the reaction between zinc and iodine to occur more easily.
- Granular zinc is mixed carefully with powdered iodine. Nothing happens.
- A drop of water is added to the mixture
- Although water is not a reactant in this reaction, water initiates a violent reaction between zinc and iodine.
Why is the water necessary for this reaction to proceed? Water is a catalyst in this reaction. Catalysts are substances that help a reaction proceed faster. They are mixed with the reactants but are not consumed in a reaction. Water allows the reaction between zinc and iodine to occur more easily.
Watch "Extreme Elephant Toothpaste" to see a dramatic representation of the decomposition of hydrogen peroxide. This time, potassium acts as a catalyst for the chemical reaction.
The Concentration of Reactants and the Rate of Chemical Reactions
The concentration of a substance refers to how much of the substance there is in a certain volume. Pouring 1 L of green food colouring into a washing machine would result in a high concentration of food colouring in the machine. Pouring 1 L of the same food colouring into a lake would result in a much lower concentration of food colouring.
The higher the concentration of reactants in a chemical reaction, the faster the reaction will occur. This makes sense, because the more of a substance there is to react with the other substance, the faster the reaction should be.
Try It!
How does the concentration of the reactants affect the reaction rate?
- DOWNLOAD this practice worksheet (S9_UB_S4_L14a_reaction_rate_conc). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
- As you watch the "Hydrogen Peroxide and the Effect of Varying Concentration" video, complete the worksheet.
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When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
1.
2. The yeast is added as a catalyst to speed up the reaction. The reaction did not start until the yeast was introduced.
3. Hydrogen = Water + Oxygen
4. H 2O2
5. 1% hydrogen peroxide will be a slower reaction than 3% hydrogen peroxide because there is less hydrogen peroxide in the solution that is able to react.
6. It is exothermic because the temperature increased.
7. Decreases
The Temperature of Reactants and the Rate of Chemical Reactions
In grade 8 science you learned about the particle theory of matter,. One of the parts of the particle theory is that all matter is made up of particles that are always moving. The energy that makes these particle move more is called heat, and we measure the average amount of heat energy using temperature. Therefore, temperature is a measure of the amount of heat energy. The higher the temperature is, the more heat energy there is, and the faster the particle of matter are moving in the substance.
If the particles are moving faster in a chemical reaction, it makes sense that they can find other particles to react with more quickly. Therefore, the rate of a chemical reaction between substances increases when the temperature of the reactants increases.
In grade 8 science you learned about the particle theory of matter,. One of the parts of the particle theory is that all matter is made up of particles that are always moving. The energy that makes these particle move more is called heat, and we measure the average amount of heat energy using temperature. Therefore, temperature is a measure of the amount of heat energy. The higher the temperature is, the more heat energy there is, and the faster the particle of matter are moving in the substance.
If the particles are moving faster in a chemical reaction, it makes sense that they can find other particles to react with more quickly. Therefore, the rate of a chemical reaction between substances increases when the temperature of the reactants increases.
Try It!
How does the temperature of the reactants affect the reaction rate?
- DOWNLOAD this practice worksheet (S9_UB_S4_L14b_reaction_rate_temp). If you prefer
to use a Google Drive or PDF version of the worksheet, click here.
-
As you watch the "Temperature and Reaction Rate" video, complete the worksheet.
-
When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
1.
2.
a. The manipulated variable is the temperature of the hydrogen peroxide solution.
b. The manipulated variable is the temperature of the hydrogen peroxide solution.
c. The controlled variables are
2.
a. The manipulated variable is the temperature of the hydrogen peroxide solution.
b. The manipulated variable is the temperature of the hydrogen peroxide solution.
c. The controlled variables are
- amount of water used (200 mL)
- amount of Alka-Seltzer used (one tablet)
3.
a. 130
b. 26°C
4. increases
5. Gas bubbles produced is evidence of a chemical change. Production of new substance (carbon dioxide) is also evidence of a chemical change.
The Surface Area of Reactants and the Rate of Chemical Reactions
The last way to increase the rate of a chemical reaction is to increase the surface area of the substances reacting. Think about how long it takes to cook a thick hamburger compared to a thin hamburger. When you put a thin hamburger on the grill almost half of all of the hamburger is touching the grill at any one time. A thick hamburger, on the other hand, takes longer because there is much hamburger on the inside that takes the heat energy awhile to reach.
The last way to increase the rate of a chemical reaction is to increase the surface area of the substances reacting. Think about how long it takes to cook a thick hamburger compared to a thin hamburger. When you put a thin hamburger on the grill almost half of all of the hamburger is touching the grill at any one time. A thick hamburger, on the other hand, takes longer because there is much hamburger on the inside that takes the heat energy awhile to reach.
Not all substances can be squished flat like hamburger. Solid substances can be broken into smaller pieces to increase surface area, and increase the rate that they can react.
Imagine a cube of sugar with side lengths of 10 cm. Each face of the cube is 10 x 10 = 100 cm2, and there are 6 faces, so the total surface area is 600 cm2.
Now split the same sugar cube into smaller, 1 cm cubes. Each of these cubes has a surface area of 1 cm x 1 cm = 1 cm2; 1 cm2 x 6 = 6 cm2. There are 10 x 10 x 10 = 1000 of these smaller cubes in the large cube, so there is now a total surface area of 6 cm2 x 1000 = 6000 cm2! That is a much greater surface area for chemical reactions than the single, large cube had. In fact, it is 10 times more.
Try It!
How does the surface area of the reactants affect the reaction rate?
- DOWNLOAD this practice worksheet (S9_UB_S4_L14c_reaction_rate_surface). If you prefer
to use a Google Drive or PDF version of the worksheet, click here.
-
As you watch the video, "Surface Area and Reaction Rate", complete the worksheet.
-
When you are satisfied with your responses you can check your work by clicking on the
"SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
1.
2.
a. The manipulated variable is the surface area of the Alka-Seltzer tablet.
b. The responding variable is the reaction rate.
c. The controlled variables are
amount of water used (250 mL)
temperature of the water used
3. increases, increases
2.
a. The manipulated variable is the surface area of the Alka-Seltzer tablet.
b. The responding variable is the reaction rate.
c. The controlled variables are
amount of water used (250 mL)
temperature of the water used
3. increases, increases
Variables in Scientific Experiemnts
You may have noticed some new terms that keep getting used as we have began to examine chemical reactions. Reactants react, and products are produced. But what about variables, such as the controlled, manipulated, and responding variables? In science, the manipulated variable is the one thing you change to see if it has an effect. The responding variable is what you measure to see what effect there might be. The controlled variables are all of the things you do not want to change.
Are you unsure of what manipulated and responding variables are? Watch "What are Science Variables?"
Need more help with variables? Apply your knowledge of variables to an experiment.
The Effect of Salt on the Boiling Temperature of Water A kettle with 200 mL of water is boiled on the stove and the temperature of the boiling water is recorded. Salt is then added to the water and the temperature of the boiling water is recorded again. Does the amount of salt dissolved in a sample of water affect the temperature that the water boils at?
The Effect of Salt on the Boiling Temperature of Water A kettle with 200 mL of water is boiled on the stove and the temperature of the boiling water is recorded. Salt is then added to the water and the temperature of the boiling water is recorded again. Does the amount of salt dissolved in a sample of water affect the temperature that the water boils at?
| Amount of Salt (g)
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Temperature of Boiling Water (°C)
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0
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96.6
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| 10 |
97.2
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| 20 | 97.7 |
| 30 | 98.1 |
| 40 |
98.8
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What are the variables in this lab experiment?
- Manipulated variable: amount of salt
- Responding variable: boiling temperature of water
- Constant variable(s): amount of water, liquid used (water), type of salt used, location, etc.
Watch
Watch "The Effect of Salt on the Boiling Point of Water".