Grades 9 and 10 | Chemistry | High School

Back to Chemistry: High School: 9th and 10th Grade

Chemistry: High School: 9th and 10th Grade Quiz - Energy from Reactions (Questions)

This Chemistry quiz is called 'Energy from Reactions' and it has been written by teachers to help you if you are studying the subject at high school. Playing educational quizzes is a user-friendly way to learn if you are in the 9th or 10th grade - aged 14 to 16.

It costs only $12.50 per month to play this quiz and over 3,500 others that help you with your school work. You can subscribe on the page at Join Us

Calculating the energy changes in chemical reactions can be a little worrying but the only math skills required are addition and subtraction... you can slip in a little multiplication if you wish!! The only chemical skill you need is to be able to work out what bonds are present in each substance but in the high school Chemistry exam, there will be plenty of clues in the question.

[readmore]

It pays to be organized, even in the exam. Take a sheet of paper and draw a vertical line down the center. The left column will be for the reactants and the right for the products. Start by writing down the individual bonds in the reactants. Next, write down how many of each bond there is. Then write down the bond energy for each one and calculate the energy contained in that number of each bond. Then work out total energy contained in the bonds of the reactants by adding the individual totals together. Do this step by step and double check at each stage to eliminate any errors.

Repeat the process for the products. Then subtract the total bond energy of the reactants from the products, paying careful attention to whether the answer is a positive or a negative number. Positive numbers mean that the reactions are endothermic, negative numbers mean that they are exothermic chemical reactions.

The questions that follow concern making and breaking bonds and the energy changes involved in doing so. To be able to complete these questions you will need the following bond energy information and a calculator:

C-H 413kJ/mol
O=O 498kJ/mol
C-O 358kJ/mol
O-H 464kJ/mol
N≡N 945kJ/mol
H-Cl 432kJ/mol
Cl-Cl 243kJ/mol
H-H 436kJ/mol
C=O 805kJ/mol
C-C 347J/mol
N-H 391kJ/mol.

Now try these ten questions on energy changes - good luck!

[/readmore]

Pick the correct combination for the correct information regarding bond energies.

[ ]	Bond breaking - Exothermic - Takes in energy Bond making - Endothermic - Gives out energy
[ ]	Bond breaking - Endothermic - Takes in energy Bond making - Exothermic - Gives out energy
[ ]	Bond breaking - Endothermic - Gives out energy Bond making - Exothermic - Takes in energy
[ ]	Bond breaking - Exothermic - Gives out energy Bond making - Endothermic - Takes in energy

The overall energy change in a chemcial reaction is -24kJ/mol. What does this tell us about the reaction?

[ ]	It is endothermic
[ ]	More energy was taken in than given out
[ ]	It is exothermic
[ ]	The temperature decreased

Using the bond energies provided, calculate the energy change for this reaction.
2CH₄ + O₂ → 2CH₃OH

[ ]	-1471kJ/mol
[ ]	-329kJ/mol
[ ]	-89kJ/mol
[ ]	+2567kJ/mol

In the Haber process, nitrogen and hydrogen are reacted together to produce ammonia. Use the bond energies provided to calculate the overall energy change in the reaction.

N₂ + 3H₂ ⇌ 2NH₃

[ ]	-93kJ
[ ]	-4599kJ
[ ]	1401kJ
[ ]	93kJ

Use the bond energies provided to calculate the energy change in the following reaction.

H₂ + Cl₂ → 2HCl

[ ]	-247kJ/mol
[ ]	-1543kJ/mol
[ ]	-185kJ/mol
[ ]	-158kJ/mol

Use the bond energies provided to calculate the energy change in the following reaction.

oxygen + hydrogen → water

[ ]	1856kJ/mol
[ ]	1370kJ/mol
[ ]	442kJ/mol
[ ]	486kJ/mol

Use the bond energies provided to calculate the amount of energy given out when propane is burnt.

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

[ ]	2054kJmol^-1
[ ]	-628kJmol^-1
[ ]	1958kJmol^-1
[ ]	-2054kJmol^-1

If ΔH for a reaction is negative, what does this tell us about the reaction?

[ ]	It is endothermic
[ ]	More energy is taken in to break bonds than is given out when bonds form
[ ]	It is exothermic
[ ]	The temperature of the reaction mixture decreases

Use the bond energy values provided to calculate ΔH for the reaction of photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Hint: For glucose (cyclical) there are the following bonds formed: 7xC-H, 5xC-C, 7xC-O and 4xO-H.

[ ]	3253kJ/mol
[ ]	-3201kJ/mol
[ ]	-6999kJ/mol
[ ]	6501kJ/mol

10.

What is the value for ΔH for respiration?

[ ]	3210kJ/mol
[ ]	-3253kJ/mol
[ ]	-6999kJ/mol
[ ]	6501kJ/mol

Chemistry: High School: 9th and 10th Grade Quiz - Energy from Reactions (Answers)

Pick the correct combination for the correct information regarding bond energies.

[ ]	Bond breaking - Exothermic - Takes in energy Bond making - Endothermic - Gives out energy
[x]	Bond breaking - Endothermic - Takes in energy Bond making - Exothermic - Gives out energy
[ ]	Bond breaking - Endothermic - Gives out energy Bond making - Exothermic - Takes in energy
[ ]	Bond breaking - Exothermic - Gives out energy Bond making - Endothermic - Takes in energy

Remember EXothermic EXit and ENdothermic ENter

The overall energy change in a chemcial reaction is -24kJ/mol. What does this tell us about the reaction?

[ ]	It is endothermic
[ ]	More energy was taken in than given out
[x]	It is exothermic
[ ]	The temperature decreased

A negative energy change shows the reaction is exothermic and so heat and/or other energy has been transferred into the surroundings, often increasing the temperature

Using the bond energies provided, calculate the energy change for this reaction.
2CH₄ + O₂ → 2CH₃OH

[ ]	-1471kJ/mol
[x]	-329kJ/mol
[ ]	-89kJ/mol
[ ]	+2567kJ/mol

When carrying out these calculations, always subtract the reactants energy from the products

In the Haber process, nitrogen and hydrogen are reacted together to produce ammonia. Use the bond energies provided to calculate the overall energy change in the reaction.

N₂ + 3H₂ ⇌ 2NH₃

[x]	-93kJ
[ ]	-4599kJ
[ ]	1401kJ
[ ]	93kJ

945 + (3x436) - (6x-391) = -93kJ

Use the bond energies provided to calculate the energy change in the following reaction.

H₂ + Cl₂ → 2HCl

[ ]	-247kJ/mol
[ ]	-1543kJ/mol
[x]	-185kJ/mol
[ ]	-158kJ/mol

Bond breaking = 436+243kJ/mol; bond making 2x432kJ/mol

Use the bond energies provided to calculate the energy change in the following reaction.

oxygen + hydrogen → water

[ ]	1856kJ/mol
[ ]	1370kJ/mol
[ ]	442kJ/mol
[x]	486kJ/mol

Add together the energy of each bond of the reactants, do the same for the bonds in the products. Then subtract the total bond energy of the reactants from that of the products to get the answer

Use the bond energies provided to calculate the amount of energy given out when propane is burnt.

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

[ ]	2054kJmol^-1
[ ]	-628kJmol^-1
[ ]	1958kJmol^-1
[x]	-2054kJmol^-1

Remember that CO₂ has 2 C=O double bonds not single bonds

If ΔH for a reaction is negative, what does this tell us about the reaction?

[ ]	It is endothermic
[ ]	More energy is taken in to break bonds than is given out when bonds form
[x]	It is exothermic
[ ]	The temperature of the reaction mixture decreases

Remember to always subtract reactants from products - the total bond energy of the products must be less than the reactants to end up with a negative answer

[x]	3253kJ/mol
[ ]	-3201kJ/mol
[ ]	-6999kJ/mol
[ ]	6501kJ/mol

Photosynthesis is an endothermic reaction and therefore ÄH is positive. LHS total = 15228kJ RHS total = 11976 LHS - RHS = ΔH

10.

What is the value for ΔH for respiration?

[ ]	3210kJ/mol
[x]	-3253kJ/mol
[ ]	-6999kJ/mol
[ ]	6501kJ/mol

Respiration is the same as photosynthesis, but in the opposite direction!!