Types of Chemical Reactions & Counting Atoms

Grade 10 Chemistry

Recall

Reactant + reactant product

Word equation

Sodium + chlorine Sodium chloride

Chemical equation

Na + Cl NaCl

Types of Reactions

Synthesis Decomposition Single-displacement Double-displacement Combustion

Synthesis Reactions

Two substances (elements) combine and form a compound

A + B C– Reactant + reactant product– Carbon + oxygen Carbon dioxide

– C + O2 CO2

Decomposition Reactions

Compound breaks down into two elements (or simpler compounds)

Reverse of synthesis C A + B

– Reactant product + product– Water hydrogen + oxygen

– 2 H2O 2H2 + O2

Single-displacement Reactions One element replaces another element in a

compound– Metal replaces a metal– Non-metal replaces a non-metal

Get a new element and a different compound A + BC AC + B

– zinc + hydrochloric acid zinc chloride + hydrogen

Double-displacement Reactions

Ions from two compounds change places– Metal replaces a metal– Non-metal replaces a non-metal

AB+ CD AD + CB– Sodium chloride + silver fluoride Sodium fluoride

+ silver chloride

Combustion Reactions

A substance reacts with oxygen to produce carbon dioxide and water

X + O2 CO2 + H2O

Reactivity Reactive - will readily take part in

chemical reactions

Reactivity A more reactive element can displace a

less reactive element in a single displacement reaction

Applies to Alkali metals (Group 1)

Reactivity Series

Reactivity Example

Single displacement reaction: Copper is more reactive than silver

Cu + AgNO3 CuNO3 + Ag

The copper displaces the silver in the compound silver nitrate

Reactivity Example Continued

Single displacement reaction: Silver is less reactive than copper

Ag + CuNO3 AgNO3 + Cu

The silver cannot displace the copper because it is less reactive. Chemical reaction does not occur

Counting Atoms

RULES FOR COUNTING ATOMS

1. SUBSCRIPTS only refer to the atom that they are BEHIND. For example…

H2SThere are TWO atoms of HYDROGEN and only ONE atom of SULFUR.

COEFFICIENTS

2. COEFFICIENTS apply to the entire compound. You MULTIPLY the coefficients and SUBSCRIPTS.

2 H2S

ATOMS OF HYDROGEN:

ATOMS OF SULFUR:

4

2

IF THERE ISN’T A SUBSCRIPT BEHIND AN ELEMENT, ASSUME THERE IS ONLY ONE ATOM OF THAT ELEMENT!

PARENTHESES

3. If elements or compounds are inside of PARENTHESES, then the SUBSCRIPT behind the parentheses applies to everything inside the parentheses.

Ba(OH)2

ATOMS OF BARIUM:

ATOMS OF OXYGEN:

ATOMS OF HYDROGEN:

1

2

2

LET’S PRACTICE!LET’S PRACTICE!

MgCl2

Atoms of Magnesium:

Atoms of Chlorine:

1

2

Al2S3

Atoms of Aluminum:

Atoms of Sulfur:

2

3

PRACTICEPRACTICE

H2SO4

Atoms of Hydrogen:Atoms of Sulfur:Atoms of Oxygen:

21

CH3OHAtoms of Carbon:

Atoms of Hydrogen:

Atoms of Oxygen:

14

4

1

THIS COULD BE A LITTLE THIS COULD BE A LITTLE TRICKY…TRICKY…

Ca3(PO4)2 Atoms of Calcium:Atoms of Phosphorus:Atoms of Oxygen:

32

Al2(SO4)3

Atoms of Aluminum:

Atoms of Sulfur:

Atoms of Oxygen:

23

8

12

Homework

Counting atoms worksheet Predict products of worksheet