Symbol equations: Flashcards
(125 cards)
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Key Points
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Symbol equations are a quick way of representing chemical reactions. They show us what atoms are involved and how they are bonded together.
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Symbol equations always take the form
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reactants → products. A + sign separates two or more reactants or products.
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State symbols are used in symbol equations to show whether each chemical is a solid
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liquid
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In a symbol equation
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what symbol is used to show a chemical reaction has taken place?
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Show answer
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Science flasks
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Video
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Watch this video to find out more about how symbol equations are used to represent and summarise
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chemical reactions
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While you’re watching
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look out for the size of the numbers used in the chemical
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formulae
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Video Transcript
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What did you notice about the size of the numbers used in the formulae?
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Show answer
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Formulae for compounds and elements
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Chemical symbols and formulae are used to represent
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elements
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and
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compounds
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for example:
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H₂ is the
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formula
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of hydrogen
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H₂SO₄ is the formula of sulfuric acid
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Mg is the symbol of magnesium
this is a symbol and not a formula because there are no numbers
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The earth's atmosphere from space
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Image caption
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The atmosphere is made up of around 78% nitrogen (N₂) and 21% oxygen (O₂). Both of these are present as molecules of two atoms bonded together.
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Chemical formulae are used to show how many of each type of
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atom
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is chemically bonded together within a substance. For example
the formula for water is H₂O which shows that each
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molecule
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is made from two hydrogen atoms bonded to one oxygen atom.
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Some
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non-metal
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elements are made from molecules. For example
hydrogen has a chemical formula of H₂
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subscripts
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and show how many atoms of that element are present.
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Other non-metal elements and all
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metal
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elements are represented by just their symbol. For example
magnesium is Mg and carbon is C.
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A sign which says 'remember'
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The word formulae is the plural of the word formula. If we're talking about more than one formula
we usually say formulae.
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The formula of ammonia is NH₃. How many nitrogen (N) and hydrogen (H) atoms are present in the molecule?
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Show answer
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Writing a symbol equation
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Chemical reactions can be represented using symbol equations. In a symbol equation
substances are written using their chemical symbol or formula.
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The formulae of the
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reactants
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always go first in a symbol equation. The reactants are separated using a + symbol.
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After the reactants
there is an arrow → to show that the chemical reaction has taken place.
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The
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products
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are written after the arrow and are also separated by + symbols.
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Example
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When carbon © is burned in air
the carbon reacts with oxygen (O₂) and carbon dioxide (CO₂) is produced.
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The symbol equation for this reaction is:
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C + O₂ → CO₂
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Compare this to the word equation:
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Carbon + oxygen → carbon dioxide
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A sign which says 'remember'
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A symbol equation should only contain symbols and formulae for the chemicals.
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Don’t use the names of the chemicals in a symbol equation. We only use the names of chemicals in word equations. Find out more about word equations in this guide.
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Test your knowledge of the different symbols used in chemical equations in this quiz.
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Quiz - What am I?
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When iron (Fe) is heated
it reacts with sulfur (S) to produce iron sulfide (FeS).
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What is the symbol equation for this reaction?
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Show answer
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Science flasks
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Using state symbols
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State symbols
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are used in symbol equations to show what state – solid
liquid
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solution
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– each substance is in.
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State State symbol
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Solid (s)
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Liquid (l)
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Gas (g)
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Aqueous solution (aq)
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State symbols are written after the formula of each substance.
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For example
compare the word equation below with its symbol equation.
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Magnesium carbonate + sulfuric acid → magnesium sulfate + water + carbon dioxide
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MgCO₃(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂O(l) + CO₂(g)
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The symbol equation shows that solid magnesium carbonate reacts with a solution of sulfuric acid to produce a solution of magnesium sulfate
plus liquid water and some carbon dioxide gas.
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Summarise the following reaction with a symbol equation
including state symbols.
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Liquid hexane (C₆H₁₄) reacts with oxygen gas (O₂). The products are carbon dioxide gas (CO₂) and liquid water (H₂O).
