Controlling chemical reactions
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
BOOK 2
OBTAINING RESOURCES
SECTION 4
CONTROLLING CHEMICAL REACTIONS
1
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
CHEMICAL REACTIONS AND HOW TO CONTROL THEM All chemical reactions involve rearranging the atoms in one group of molecules to form new molecules. This is how new products are made. It is important to remember that during a chemical reaction and the formation of new products, no atoms are lost or gained. To create new products and to rearrange atoms, energy is required to break bonds that hold the atoms together and energy is released when bonds are built in the new products. If the energy released from breaking bonds is greater than the energy needed to create new bonds then the reaction is exothermic. This means energy is released to the surroundings and the reaction vessel feels hot. If the energy released from breaking bonds is less than the energy needed to create new bonds then the reaction is endothermic. This means energy is taken from the surroundings and the reaction vessel feels cold.
In an exothermic reaction, energy
In an endothermic reaction,
is released into the surroundings
energy is absorbed from the
as heat. As a result, the
surroundings. As a result, the
temperature of the surroundings
temperature of the surroundings
increases.
drops.
2
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
RATES OF REACTION The rate of a reaction is a measure of how fast the reactants are used up or products are formed. The rate of a reaction can be increased in the following 4 ways: •
increasing the concentration
•
increasing the surface area of solids
•
increasing the pressure
•
increasing the temperature
Hydrogen ions can hit the outer layer of atoms ... ... but not these in the centre of the lump.
With the same number of atoms now split into lots of smaller bits, there are hardly any magnesium atoms which the hydrogen ions can’t get at.
All of the above increase the chance of a particle collision with enough energy for a reaction to take place. Increasing the surface area of a solid means that there are fewer particles being sheltered by other particles, allowing more successful collisions.
3
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
Increasing the pressure forces the particles closer together. As they are still moving at the same speed there is more chance of a successful collision.
Increasing the temperature increases the speed particles move because they gain more energy. Faster moving particles means that they collide more often with more force, speeding up the reaction.
4
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
Increasing the concentration means increasing the number of particles which can react. This increases the chances of successful collision, speeding up the reaction.
5
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
ACTIVITY
The effect of concentration on the reaction between sodium thiosulfate and the hydrochloric acid.
METHOD:
DIAGRAM:
You will use different concentrations of sodium thiosulfate: 1. 50 cm3 sodium thiosulfate.
thiosulfate
2. 25 cm sodium thiosulfate and 3
25 cm3 water. 3. 10 cm3 sodium thiosulfate and 40 cm3 water.
stop clock 5 cm3 hydrochloric acid
Measure the time it takes for the cross to disappear each time the hydrochloric acid is added to the sodium thiosulfate mixture.
RESULTS: Volume of sodium thiosulfate (cm3)
Volume of water (cm3)
Volume of HCl (cm3)
50
0
5
25
25
5
10
40
5
6
Time for the cross to disappear (s)
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
ACTIVITY 2
The effect of temperature on the reaction between sodium thiosulfate and hydrochloric acid.
METHOD:
DIAGRAM:
You will use the same concentrations of sodium thiosulfate at three different temperatures: thiosulfate
1. Room temperature (about 20 °C)
you will need to measure this
with a thermometer
2. 40 °C
stop clock
3. 60 °C
5 cm3 hydrochloric acid
Measure the time it takes for the cross to disappear each time the hydrochloric acid is added to the conical flask with the sodium thiosulfate mixture. RESULTS: Volume of sodium thiosulfate (cm3)
Volume of HCl (cm3)
Temperature(°C)
50
5
20
50
5
40
50
5
60
7
Time for the cross to disappear (s)
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
ACTIVITY 3
The effect of surface area (particle size) on the reaction between calcium carbonate and hydrochloric acid.
DIAGRAM: Car Carbon Dioxide Gas
Clamp Measuring cylinder
Delivery tube Marble chips
Trough Water
Dilute acid
METHOD: You will use the same volume (25 cm3) of hydrochloric acid (HCl). You will use the same mass (0.5 g) of marble chips (calcium carbonate). Measure the volume of CO2 given off in each of the following reactions: 1. With whole marble chips. 2. With crushed marble chips/powdered calcium carbonate.
8
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
RESULTS :
Time (minutes)
Volume of CO2 produced
Volume of CO2 produced
with chips (cm3)
with powder (cm3)
1
2 3 4 5 6 7 8 9 10 11 12
9
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
FOR ALL OF THE ACTIVITIES WRITE A SIMPLE CONCLUSION.
10
BOOK 2
OBTAINING RESOURCES
SECTION 4
CONTROLLING CHEMICAL REACTIONS
1
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
CHEMICAL REACTIONS AND HOW TO CONTROL THEM All chemical reactions involve rearranging the atoms in one group of molecules to form new molecules. This is how new products are made. It is important to remember that during a chemical reaction and the formation of new products, no atoms are lost or gained. To create new products and to rearrange atoms, energy is required to break bonds that hold the atoms together and energy is released when bonds are built in the new products. If the energy released from breaking bonds is greater than the energy needed to create new bonds then the reaction is exothermic. This means energy is released to the surroundings and the reaction vessel feels hot. If the energy released from breaking bonds is less than the energy needed to create new bonds then the reaction is endothermic. This means energy is taken from the surroundings and the reaction vessel feels cold.
In an exothermic reaction, energy
In an endothermic reaction,
is released into the surroundings
energy is absorbed from the
as heat. As a result, the
surroundings. As a result, the
temperature of the surroundings
temperature of the surroundings
increases.
drops.
2
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
RATES OF REACTION The rate of a reaction is a measure of how fast the reactants are used up or products are formed. The rate of a reaction can be increased in the following 4 ways: •
increasing the concentration
•
increasing the surface area of solids
•
increasing the pressure
•
increasing the temperature
Hydrogen ions can hit the outer layer of atoms ... ... but not these in the centre of the lump.
With the same number of atoms now split into lots of smaller bits, there are hardly any magnesium atoms which the hydrogen ions can’t get at.
All of the above increase the chance of a particle collision with enough energy for a reaction to take place. Increasing the surface area of a solid means that there are fewer particles being sheltered by other particles, allowing more successful collisions.
3
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
Increasing the pressure forces the particles closer together. As they are still moving at the same speed there is more chance of a successful collision.
Increasing the temperature increases the speed particles move because they gain more energy. Faster moving particles means that they collide more often with more force, speeding up the reaction.
4
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
Increasing the concentration means increasing the number of particles which can react. This increases the chances of successful collision, speeding up the reaction.
5
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
ACTIVITY
The effect of concentration on the reaction between sodium thiosulfate and the hydrochloric acid.
METHOD:
DIAGRAM:
You will use different concentrations of sodium thiosulfate: 1. 50 cm3 sodium thiosulfate.
thiosulfate
2. 25 cm sodium thiosulfate and 3
25 cm3 water. 3. 10 cm3 sodium thiosulfate and 40 cm3 water.
stop clock 5 cm3 hydrochloric acid
Measure the time it takes for the cross to disappear each time the hydrochloric acid is added to the sodium thiosulfate mixture.
RESULTS: Volume of sodium thiosulfate (cm3)
Volume of water (cm3)
Volume of HCl (cm3)
50
0
5
25
25
5
10
40
5
6
Time for the cross to disappear (s)
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
ACTIVITY 2
The effect of temperature on the reaction between sodium thiosulfate and hydrochloric acid.
METHOD:
DIAGRAM:
You will use the same concentrations of sodium thiosulfate at three different temperatures: thiosulfate
1. Room temperature (about 20 °C)
you will need to measure this
with a thermometer
2. 40 °C
stop clock
3. 60 °C
5 cm3 hydrochloric acid
Measure the time it takes for the cross to disappear each time the hydrochloric acid is added to the conical flask with the sodium thiosulfate mixture. RESULTS: Volume of sodium thiosulfate (cm3)
Volume of HCl (cm3)
Temperature(°C)
50
5
20
50
5
40
50
5
60
7
Time for the cross to disappear (s)
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
ACTIVITY 3
The effect of surface area (particle size) on the reaction between calcium carbonate and hydrochloric acid.
DIAGRAM: Car Carbon Dioxide Gas
Clamp Measuring cylinder
Delivery tube Marble chips
Trough Water
Dilute acid
METHOD: You will use the same volume (25 cm3) of hydrochloric acid (HCl). You will use the same mass (0.5 g) of marble chips (calcium carbonate). Measure the volume of CO2 given off in each of the following reactions: 1. With whole marble chips. 2. With crushed marble chips/powdered calcium carbonate.
8
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
RESULTS :
Time (minutes)
Volume of CO2 produced
Volume of CO2 produced
with chips (cm3)
with powder (cm3)
1
2 3 4 5 6 7 8 9 10 11 12
9
OBTAINING RESOURCES - SECTION 4 CONTROLLING CHEMICAL REACTIONS
FOR ALL OF THE ACTIVITIES WRITE A SIMPLE CONCLUSION.
10
