Types of Reactions

Question 1

What are combination reactions?

Answer 1

A + B —-> AB
Where atoms of a different substance combine to form only one product.
Heat is required to start most combination reactions.
[compounds] are formed.

Question 2

EXAMPLE OF A COMBINATION REACTION

Answer 2

Rusting, iron atoms react with oxygen atoms (from the air) to form a new substance, iron oxide.
iron + oxygen —> iron oxide
Fe + O2 —> FeO

Burning magnesium ribbon in air (oxygen) to form white powder of magnesium oxide.
magnesium + oxygen –> magnesium oxide
2Mg + O2 –> 2MgO

Question 3

Why do atoms combine?

Answer 3

Atoms combine to become stable. All elements (except those in group 18) are considered to be in an active/reactive state as they do not have a full valence shell of electrons. So, they combine with other atoms to achieve a full shell, become ions, and hence become stable and do not react further.

Question 4

What can combine with what? What does it create?

Answer 4

metal + non-metal —> ionic compound
non-metal + non-metal —-> covalent compound
OXIDATION! Where elements combine quickly with oxygen.

give examples
H2 + O2 —> H2O
H2 + O2 —-> H2o2

Question 5

What happens when Cu and O react?

Answer 5

When Cu and O react, product forms in two phases. In each phase the product displays different oxidation state.

Outer surface = black tarnish
Inner surface = deep red tarnish.

Question 6

Give examples of types of combination reactions.

Answer 6

Oxidation = where elements combine quickly with oxygen.

Combustion = a very fast oxidation. Product is formed quickly with heat energy.

Rusting = slow oxidation, no heat required. Product formed but slower than combustion.

Question 7

What is thermal decomposition?

Answer 7

If sufficient heat energy is applied, an ionic compound will break up into it’s ions.

AB —> A + B (decomposition)

Question 8

List the types of decomposition reactions

Answer 8

metal carbonate + heat —> metal oxide + co2
metal bicarbonate + heat —> metal oxide + water + co2
metal hydroxide + heat —-> metal oxide + water
metal hydrogen carbonate —> metal carbonate + co2 + water

Question 9

When would you test for water?

Answer 9

Once a bicarbonate or hydroxide has decomposed; it is very likely that one of the products is water. To test for H2O, place a piece of cobalt chloride paper in it. It will turn from BLUE to PINK.

Question 10

What are the rules surrounding decomposition?

Answer 10

1. Metal carbonates and hydroxides that from from less reactive metals: decompose easily.
2. Metal carbonates and metal hydroxides that form from more reactive metals do not decompose easily.
3. All metal hydrogen carbonates decompose readily

Question 11

Explain what is meant by a precipitate

Answer 11

A solid formed when solutions containing the ions of an insoluble substance are mixed.

Question 12

Explain what is meant by a soluble substance

Answer 12

A substance which dissolves readily in water.

Question 13

Explain what is meant by an insoluble substance

Answer 13

A substance that will not dissolve readily in water.

Question 14

Explain what is meant by a spectator ion

Answer 14

An ion which does not take part in a chemical reaction.

Question 15

Explain what is meant by a precipitation reaction

Answer 15

A reaction where ions are exchanged between soluble substances and an insoluble substance (solid/precipitate) is formed.

Question 16

Describing combination reactions… (heat used)

Answer 16

the mixture of ___ (colour) and ___ (colour) reacts with a bright glow to form a ___ (colour).

Question 17

Describing precipitation reactions…

Answer 17

When __ (colour) is added to ___ (colour) a ____ (colour) precipitate forms and a ___ (colour) solution of ___.

Question 18

What is a displacement reaction?

Answer 18

A metal higher on the reactivity series displaces a metal ion in solution lower on the reactivity series.

Question 19

Describing decomposition reactions…

Answer 19

A single reactant forms two products.

Question 20

Describe the reaction that takes place when a small amount of solid manganese dioxide is added to hydrogen peroxide.

Answer 20

The colourless solution of hydrogen peroxide, when black manganese dioxide is added, would produce a colourless liquid of water, and bubbles of colourless oxygen gas would form. It would get warm.

Question 21

What is catalytic decomposition?

Answer 21

A compound is broken down (decomposed) into its consistent elements by a catalyst.

Question 22

Describe the decomposition reaction of H2O2 with and without a catalyst

Answer 22

Without:
- The reaction processes very slowly at room temperature
- Volume of product (same)produced slower
Reactants take a longer time to get used up

WITH:

• The reaction begins rapidly and vigorously to produce a lot of colourless gas
• Volume of product (same) produced faster