What is meant by the activation energy in a chemical reaction?
The total energy used up when a reaction has stopped.
The energy absorbed during a reaction.
The energy released during a reaction.
The minimum energy needed for a reaction to occur.
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What is the activation energy for a reaction?
The difference between the energy of the reactants and the products
The energy needed for a reaction to start
The energy of the reactants
The energy of the products
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Which reaction profile has an arrow showing the activation energy?
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A student adds a small amount of ammonium chloride to a beaker of water. The temperature of the water decreases from 21 oC to 17 oC.
Which type of reaction has occurred and why?
| type of reaction | reason |
A | exothermic | heat is released |
B | exothermic | heat is absorbed |
C | endothermic | heat is released |
D | endothermic | heat is absorbed |
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The graph below shows a reaction profile for the reaction between methane and oxygen.
What does the label X represent?
Activation energy
Overall energy change
Reactants
Progress of the reaction
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The graph below shows a reaction profile for the reaction between methane and oxygen.
What does the label X represent?
Activation energy
Overall energy change
Reactants
Progress of the reaction
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Which is true about chemical energy changes?
| Reaction type | Energy flows | Temperature of surroundings |
A | exothermic | to the surroundings | increases |
B | exothermic | from the surroundings | decreases |
C | endothermic | to the surroundings | decreases |
D | endothermic | from the surroundings | increases |
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1 markThe reaction profile for making nitrogen monoxide, NO, is shown below:
What is the activation energy for this reaction?
+140 kJ
+180 kJ
+320 kJ
-330 kJ
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Which statement is true about exothermic and endothermic reactions?
The products have more energy than the reactants in an exothermic reaction
The products have more energy than the reactants in an endothermic reaction
The activation energy for an exothermic reaction is always larger than the activation energy for an endothermic reaction
Most reactions are endothermic
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Look at the energy changes in the reaction profile for the reaction between hydrogen and chlorine
Which energy change shows the overall energy change of the reaction?
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1 markChlorine reacts with methane in sunlight.
CH4 + Cl2 → CH3Cl + HCl
The diagram below shows the displayed formulae for the reaction of chlorine with methane.
The table below shows the bond energies and the overall energy change in the reaction.
| C-H | Cl-Cl | C-Cl | H-Cl | Overall energy change |
Energy in kJ/mol | 413 | 243 | X | 432 | -122 |
What is the value of X?
67 kJ
134 kJ
346 kJ
542 kJ
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1 markHow much energy is needed to break all the bonds in 0.025 g of nitrogen gas?
The relative atomic mass, Ar, of N is 14.
Bond | Bond energy in kJ/mol |
N | 945 |
1701 J
1701 kJ
844 J
844 kJ
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An energy level diagram is shown below.
Which row is correct for the points labelled 1, 2 and 3?
| 1 | 2 | 3 |
A | activation energy | energy change | reactants |
B | energy change | activation energy | products |
C | energy change | activation energy | reactants |
D | activation energy | energy change | products |
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Higher tier only
Chlorine and ethane react together in an exothermic reaction to produce chloroethane and hydrogen chloride. The equation for the reaction is shown below.
C2H6 + Cl2 → C2H5Cl + HCl
The table below shows the relevant bond energies.
bond | bond energy / (kJ / mol) |
CーCl | + 340 |
CーC | + 350 |
CーH | + 410 |
ClーCl | + 240 |
HーCl | + 430 |
What is the overall energy change for the reaction between chlorine and ethane?
-120 kJ / mol
-1020 kJ / mol
+120 kJ / mol
+1020 kJ / mol
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Higher tier only
The production of ammonia involves the exothermic reaction between nitrogen and hydrogen. The equation for the reaction is shown.
N2 + 3 H2 → 2 NH3
The table shows the bond energies.
bond | bond energy / (kJ / mol) |
NーH | +390 |
HーH | +436 |
N☰N | +945 |
What is the energy released during the reaction?
-230 kJ / mol
-1025 kJ / mol
-87 kJ / mol
+87 kJ / mol
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