In this lesson, we will learn:
• To analyze chemical reactions in terms of the reactants and products involved.
• To understand the value of categorizing reactions in chemistry.
• To predict the products of chemical reactions based on the reactants involved.
• A lot of chemical reactions can be categorized by the reactants they use or the products they form. There are many types including neutralization, combustion, displacement, decomposition and metathesis. This is useful to predict the requirements and outcomes of a reaction you’re doing!
• Neutralization reactions are identified by the use of an acid and an alkali. ∘ An acid can normally be spotted by the formula beginning with H (such as HCl, H2SO4 or HNO3). ∘ An alkali can likewise normally be spotted by the formula ending in OH as a group (such as NaOH, Ca(OH)2 etc) ∘Neutralization reactions produce water and a salt, made of the metal ion(s) of the alkali and the negative ion(s) of the acid involved. These are the remaining compound fragments that did not form water. ∘ An example of a neutralization reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) is below:
HCl + NaOH → NaCl + H2O
• Combustion reactions are defined by the use of oxygen gas to react with one other chemical. ∘Combustion of hydrocarbons is a very common reaction, and is how most cars generate power. ∘Combustion is technically any reaction with oxygen. Some good evidence for a combustion reaction is a compound of oxygen in the products that wasn’t in the reactants. ∘ You can think of combustion as a chemical name for ‘burning’ – it is technically any reaction with oxygen. ∘ An example of a combustion reaction with pentane, C5H12, is below:
C5H12+ 8O2 → 5CO2+ 6H2O
• Displacement reactions involve an atom or groups of atoms being exchanged or ‘swapped’ from a chemical compound. ∘ Displacement reactions involve a metal (or non-metal) in elemental form e.g. Mg (or Cl2) and a metal (or non-metal) in a salt (e.g. ZnBr2) where the two metals (or non-metals) exchange. ∘ An example of a displacement between two non metals (chlorine and bromine) is below:
Cl2+MgBr2 → MgCl2+ Br2
• Metathesis reactions involve atoms or groups of atoms being exchanged between two different chemical compounds containing both metal and non-metal ions. ∘ Metathesis is similar to a displacement reaction except two compounds are displaced, not one. For this reason metathesis reactions are sometimes called double displacements. ∘ An example of a metathesis reaction is below:
BaCl2+ 2 AgNO3 → Ba(NO3)2+ 2 AgCl
• Decomposition reactions involve one chemical compound reactant breaking down into two or more products which were originally part of the starting material. ∘ Decomposition reactions are easy to spot – they normally only have one reactant which is the compound that is decomposing! ∘ An example of a decomposition reaction is below:
2H2O2 → 2H2O + O2
Spotting chemical patterns
Recall the main types of chemical reactions and how to identify them.
Four reactions are shown below:
Reaction 1: C5H12(l)+8 O2(g)→5 CO2(g)+6 H2O(g)
Reaction 2: ZnSO4(aq)+Mg(s)→MgSO4(aq)+Zn(s)
Reaction 3: CaCO3(s)→CaO(s)+CO2(g)
Reaction 4: AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)
Balance equations and identify the type of reaction taking place.
Balance and categorise the following equations:
Apply knowledge of reaction types to predict products, balance equations and categorise the reaction.
Complete and balance the reaction equations, then categorise them.
Types of chemical reactions
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