Chemical Reactions Cheatsheet | Year 11 Chemistry

Read the complete list of the 29 chemical reactions year 11 students must know for HSC Chemistry. Ace your Chemistry exam with this free cheatsheet.

Having trouble keeping track of all the chemical equations you need to learn? Here is the complete list of all the chemical reactions year 11 students must know for the HSC.

In this article, we cover


General Chemical Reactions

Synthesis reactions

Synthesis reaction involves the formation of a complex product from two simpler reactants.

A + B → AB

eg. 2C(s) + O2(g) → 2CO(g)


Decomposition reactions

Decomposition reactions are the opposite of synthesis reactions. A complex reactant decomposes into simpler products.

AB → A + B

eg. H2CO3(aq) → CO2(g) + H2O(l)


Precipitation reactions

Precipitation reactions occur when two aqueous solutions combine to form an insoluble salt.

AB(aq) + CD(aq)  → AD(s) + CB(aq) 

eg. AgNO3(aq) + KI(aq) → AgI(s) + KNO3(aq)


Combustion Reaction

Complete combustion of hydrocarbon

hydrocarbon  + oxygen → carbon dioxide + water

eg. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)


Incomplete combustion of hydrocarbon

Incomplete combustion produces water and a combination of carbon soot and/or carbon monoxide.

hydrocarbon + oxygen → water + carbon soot + carbon monoxide

eg. 4CH4(g) + 5O2(g) →  8H2O(l) + 2C(s) + 2CO(g)


hydrocarbon + oxygen → water + carbon soot

eg. CH4(g) + O2(g) →  2H2O(l) + C(s) 


hydrocarbon + oxygen → water + carbon monoxide

eg. 2CH4(g) + 3O2(g) →  4H2O(l) + 2CO(g) 


Reactions with Acids

Acid / base reaction

Acids react with bases to form a salt and water. This is also referred to as a neutralisation reaction.

acid + base → water + salt

eg. HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)


Acid / carbonate reaction

Acids react with metal carbonates to form water, carbon dioxide and a salt.

acid + carbonate → water + salt + carbon dioxide

eg. 2HCl(aq) + Na2CO3(aq) → H2O(l) + 2NaCl(aq) + CO2(g) 


Acid / metal reaction

Metals react with dilute acids to form a metal salt and hydrogen gas.

acid + metal → salt + hydrogen gas

eg. Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)


Reactions with Metals

Reaction of metal with liquid water

Generally, when metals react with liquid water, a metal hydroxide and hydrogen gas are produced

metal + liquid water → metal hydroxide + hydrogen gas

eg. Na(s) + H2O(l) → NaOH(aq) + H2(g) 


Reaction of metal with gaseous water

Generally, when metals react with steam, a metal oxide and hydrogen gas is produced.

metal + steam → metal oxide + hydrogen gas

eg. Zn(s) + H2O(g) → ZnO(s) + H2(g) 


Reaction of metal with oxygen

Metals react with oxygen gas in a combustion reaction to form metal oxides

metal + oxgen → metal oxide

2Mg(s) + O2(g) → 2MgO(s)


Redox Reactions

Redox reactions involve the transfer of electrons. One chemical species loses electrons and is oxidised while the other species gains electrons and is reduced.

Displacement reaction

Displacement reactions are a class of redox reactions and can be represented as a full equation:

2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)


Net ionic equation

Displacement reactions can also be written as net ionic equations, where the spectator ions are removed

2Al(s) + 6H+(aq) → 2Al3+(aq) + 3H2(g)


Half equation

A redox reaction can be also represented using a pair half-equations to show the loss and gain of electrons

2Al(s) → 2Al3+(aq) + 6e (oxidation)

6H+(aq) + 6e →3H2(g)  (reduction)

When writing half equations don’t forget to balance both the number of atoms and charge


Photosynthesis and Respiration


In the presence of sun light, carbon dioxide and water is converted to glucose and oxygen.

carbon dioxide + water + energy → glucose + oxygen 

6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)


Cellular Respiration

Cellular respiration is the reverse of photosynthesis. Glucose and oxygen react to form water and carbon dioxide. This process releases energy.

glucose + oxygen → water + carbon dioxide + energy 

C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l)


Reactions in Chemical Tests

Lime water test for carbon dioxide

A common way to test for the presence of carbon dioxide is by bubbling the gas through lime water Ca(OH)2 which is clear and colourless. If carbon dioxide is present, it will react with the lime water to form white calcium carbonate as a precipitate. The solution will turn a cloudy white.

calcium hydroxide + carbon dioxide → calcium carbonate + water

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)


Hydrogen pop test

To test for the presence of hydrogen gas, hold a lit match above a sealed test tube. If a pop is heard, when the seal is removed, this indicates the presence of hydrogen gas.

2H2(g) + O2(g) → 2H2O(l)


Nuclear Reactions

Alpha decay

Alpha decay involves the emission of an alpha particle ^4_2He .

^A_ZX \rightarrow  ^{A-4}_{Z-2} X +  ^4_2He


^{235}_{92}U \rightarrow  ^{231}_{90}Th +  ^4_2He


Beta decay

Beta decay involves the emission of a beta particle ^0_{-1}e .

^A_ZX \rightarrow  ^{A}_{Z+1} X +  ^0_{-1}e^-1


^{14}_{12}C \rightarrow  ^{14}_7N +  ^0_{-1}e^- 


Gamma decay

During gamma decay, an excited nucleus releases energy through the emission of a gamma ray.

^A_ZX^* \rightarrow  ^A_ZX + \gamma


^{137}_{56} Ba^* \rightarrow  ^{137}_{56} Ba + \gamma



Written by Hee-Chan Jang

Hee-Chan is the author of Chemistry resources on Learnable. He loves teaching and helping students to "learn smarter", using his multidisciplinary knowledge of science and engineering. He is also currently completing his doctoral degree in mineral processing at The University of Sydney.

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