Chemical Reactions Tutorial Questions

Chemical Reactions Tutorial Questions:

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 reaction has taken place.

4) All reactions have one thing in common: there is a rearrangement of chemical bonds.

5) Chemical reactions always involve the breaking of bonds, forming of bonds, or both.

6) In all reactions we still have all of the original atoms at the end that we had at the start.

7) In every reaction there can never be any missing atoms or new atoms.

8) Chemical reactions only rearrange bonds in the atoms that are already there.

9) 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 leftover.  However, this reaction only makes H2O.

10) 2 H2  + O2 = 2 H2O
Which is also 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 (in the reactants) and after the reactions (in the products).

13) What is the balanced equation for this reaction? 2Cu + O2 = 2CuO

14) In the unbalanced equation there are:
Reactants:                      Products:
Cu atoms = 1                 Cu atoms = 2
O atoms = 2                   O atoms = 2

15) To balance this equation we have to add 1Cu atom to the products because this reaction doesn't make lone oxygen atoms.

16) When we added a molecule of CuO, now the number of O atoms is balanced but the number ofCu atoms don't match.  No we have to add more Cu atoms to the reactants.

17) The balanced equation for this reaction is:
2Cu + O2 = 2CuO
Which is the same thing as:
# of reactants                    Products
2 Cu atoms                      2 Cu atoms
2 oxygen atoms               2 O atoms

18) The balanced equation for this reaction is:
CH4  + 2O2 --> H2O + CO2

19) The balanced equation for this reaction is:
1N2 + 3H2 = 2 NH3

20) The balanced equation for this reaction:
2KCIO3 = 2KCI + 3O2

21) The balanced equation for this reaction:
4Al + 3O2 = 2Al2O3

Summary:
1) Chemical reactions always involve forming bonds, breaking bonds, or both.

2) The Law of Conservation of Mass says that the same atoms must be present before and after the reaction.

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.