Chemical Reactions Tutorial Questions and Answers:
1. Starting materials in a chemical reaction are called
Reactants
2. The ending materials in a chemical reaction are called
Products
3. The arrow indicates a
Chemical change has taken place.
4. All reactions have one thing in common: there is a
Rearrangement of the bonds
5. Chemical reactions always involve
breaking bonds, forming bonds, or both
6. In all reactions we still have all of the
same atoms when the reaction is over that we had in the start
7. In every reaction there can never be any
missing atoms or new atoms when the reaction is over
8. Chemical reactions only
rearrange the bonds in the atom that are already there
9. Let’s represent a reaction on paper. For example, hydrogen gas (H2) reacts with oxygen gas (O2) to form water (H2O):
If we use only the atoms shown, we’d have 2 atoms of H and 2 atoms of O as reactants. This would make 1 molecule of H2O, but we'd have 1 atom of O left over. However this reaction only makes H2O.
10. So to make H2O from oxygen gas and hydrogen gas, the balanced equation would be:
Which is the same as:
11. This idea is called the
Law of Conservation of Mass
12. There must be the same mass and the same number of atoms before the reaction and after the reaction.
13. What is the balanced equation for this reaction?
2 Cu + 2 O2 = 2 CuO
14. In the unbalanced equation there are:
15. To balance this equation, we have to add 2 molecules to the products, because this reaction doesn’t make lone O atoms.
16. When we added a molecule of CuO, now the number of product atoms is balanced but the number or reactant atoms don’t match. Now we have to add more Cu atoms to the reactants.
17. The balanced equation for this reactions is:
This is the same thing as saying:
18. What is the balanced equation for this reaction?
19. What is the balanced equation for this reaction?
20. What is the balanced equation for this reaction?
21. What is the balanced equation for the reaction?
1. Starting materials in a chemical reaction are called
Reactants
2. The ending materials in a chemical reaction are called
Products
3. The arrow indicates a
Chemical change has taken place.
4. All reactions have one thing in common: there is a
Rearrangement of the bonds
5. Chemical reactions always involve
breaking bonds, forming bonds, or both
6. In all reactions we still have all of the
same atoms when the reaction is over that we had in the start
7. In every reaction there can never be any
missing atoms or new atoms when the reaction is over
8. Chemical reactions only
rearrange the bonds in the atom that are already there
9. Let’s represent a reaction on paper. For example, hydrogen gas (H2) reacts with oxygen gas (O2) to form water (H2O):
H2 +O2 = H2O
If we use only the atoms shown, we’d have 2 atoms of H and 2 atoms of O as reactants. This would make 1 molecule of H2O, but we'd have 1 atom of O left over. However this reaction only makes H2O.
10. So to make H2O from oxygen gas and hydrogen gas, the balanced equation would be:
2 H2 + 1 O2 = 2 H2O
Which is the same as:
| # of atoms in Reactants | Element | # of Atoms in Products |
| 4 | H | 4 |
| 2 | O | 2 |
11. This idea is called the
Law of Conservation of Mass
12. There must be the same mass and the same number of atoms before the reaction and after the reaction.
13. What is the balanced equation for this reaction?
2 Cu + 2 O2 = 2 CuO
14. In the unbalanced equation there are:
| Reactants | Products |
| Cu atoms 1 | Cu atoms 1 |
| O atoms 2 | O atoms 1 |
15. To balance this equation, we have to add 2 molecules to the products, because this reaction doesn’t make lone O atoms.
16. When we added a molecule of CuO, now the number of product atoms is balanced but the number or reactant atoms don’t match. Now we have to add more Cu atoms to the reactants.
17. The balanced equation for this reactions is:
2 Cu + 2 O2 = 2 CuO
This is the same thing as saying:
| Reactants | Products |
| 2 Cu atoms | 2 Cu atoms |
| 2 O atoms | 2 O atoms |
18. What is the balanced equation for this reaction?
1 CH4 + 2 O2 = 2 H2O + 1 CO2
# of atoms in Reactants | Element | # of atoms in Products |
1 | C | 1 |
4 | H | 2 |
2 | O | 3 |
19. What is the balanced equation for this reaction?
1 N2 + 3 H2 = 2 NH2
# of atoms in Reactants | Element | # of atoms in Products |
2 | N | 1 |
2 | H | 3 |
20. What is the balanced equation for this reaction?
2 KCIO3 = 2 KCI + 3 O2
# of atoms in Reactant | Element | # of atoms in Products |
1 | K | 1 |
1 | CI | 1 |
3 | O | 2 |
21. What is the balanced equation for the reaction?
4 AI + 6 O2 = 2 AI2O3
# of atoms in Reactants | Element | # of atoms in Products |
1 | AI | 2 |
2 | O | 3 |
Summary:
1. Chemical reactions always involve breaking bonds, making bonds, or both.
2. The Law of Conservation of Mass says that the same atoms must be rearranged.
3. To balance a chemical equation, you change the coefficients in front of each substance until there are the same number of each type of atom in both reactants and products.
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