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 SUBSCRIPTS only refer to the atom that they are BEHIND. For example… H2S There are TWO atoms of HYDROGEN and only ONE atom of SULFUR.

COEFFICIENTS 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! MgCl2 Atoms of Magnesium: Atoms of Chlorine: 1 2 Al2S3 Atoms of Aluminum: Atoms of Sulfur: 2 3

PRACTICE 2 1 4 CH3OH 1 4 1 H2SO4 Atoms of Hydrogen: Atoms of Sulfur: Atoms of Oxygen: 2 1 4 CH3OH Atoms of Carbon: Atoms of Hydrogen: Atoms of Oxygen: 1 4 1

THIS COULD BE A LITTLE TRICKY… Ca3(PO4)2 Atoms of Calcium: Atoms of Phosphorus: Atoms of Oxygen: 3 2 8 Al2(SO4)3 Atoms of Aluminum: Atoms of Sulfur: Atoms of Oxygen: 2 3 12

Homework Counting atoms worksheet Predict products of worksheet