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End of chapter exercises

For each of the following definitions give one word or term:

  1. A change that can be seen or felt, where the particles involved are not broken up in any way

  2. The formation of new substances in a chemical reaction

  3. A reaction where a new product is formed from elements or smaller compounds

a) Physical change

 

b) Chemical change

 

c) Synthesis reaction

Explain how a chemical change differs from a physical change.

In a physical change the particles may rearrange themselves but do not break up. A chemical change involves the breaking up of some particles and the formation of new particles.

 

Physical changes have very small energy changes while chemical changes have very large energy changes.

 

Chemical changes are more difficult to reverse compared to physical changes.

Complete the following table by saying whether each of the descriptions is an example of a physical or chemical change:

Table 1

Description

Physical or chemical

hot and cold water mix together

 

milk turns sour

 

a car starts to rust

 

food digests in the stomach

 

alcohol disappears when it is placed on your skin

 

warming food in a microwave

 

separating sand and gravel

 

fireworks exploding

 

Description

Physical or chemical

Hot and cold water mix together

Physical

Milk turns sour

Chemical

A car starts to rust

Chemical

Food digests in the stomach

Chemical

Alcohol disappears when it is placed on your skin

Physical

Warming food in a microwave

Physical

Separating sand and gravel

Physical

Fireworks exploding

Chemical

 

For each of the following reactions, say whether it is an example of a synthesis or decomposition reaction:

  1. NH 4 2 CO 3 NH 3 +CO 2 +H 2 O

  2. N 2 g+3H 2 g2NH 3 (g)

  3. CaCO 3 CaO+CO 2

a) Decomposition

b) Synthesis

c) Decomposition

For the following equation: CaCO 3 sCaO+CO 2 show that the law of conservation of mass applies. Draw sub-microscopic diagrams to represent this reaction.

Left hand side of the equation

Total atomic mass=(1×40)+(1×12)+(3×16)=100 u

Right hand side of the equation

Total atomic mass=(1×12)+(2×16)+(1×40)+(1×16)=100 u

Using submicroscopic diagrams we get:

CaCO3_submicro.png

Note that calcium carbonate is an ionic substance and so the representation here is a simplified form of the crystal lattice structure. The calcium ion is ionically bonded to the carbonate ion.