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Presentation On Stoichiometry: Chemical Reactions

Published in: Chemistry | Science
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This PPT is suitable for the IGCSE and O Level Chemistry students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Chemical Reactions Chemistry (IGCSE / O-Level)
  2. What will you learn in this lesson? • Word equation • Balanced symbol equation • State symbols • Ionic equations
  3. Word Equation A summary of a chemical reaction using the chemical names of the reactants and products magueSium oxide product Chemical equations do not include the amount of heat absorbed or released during the reaction
  4. Balanced Symbol Equation A summary of a chemical reaction using chemical formulae — the total number of any elements involved is the same on both reactant and product sides of the equation It is summed up in a law of conservation of mass. It states that the total mass of all the products of a chemical reaction is equal to the total mass of all the reactants 2+-12 water 2HP Summary of the reaction between hydrogen and oxygen,
  5. Balanced Symbol Equation (contd.) Balanced equation for reaction between Magnesium and Oxygen forming Magnesium Oxide: Step 1. Make sure you know what the reactants and products are. For example, magnesium burns In alr (oxygen) to form magnesium oxide. Step 2. Frorn this you can write out the word equation: magnesium + oxygen magnesium oxide Step 3. Write out the equation using the formulae of the elements and compounds: mg + 02 mgo Remember that oxygen exists as diatomic molecules. ms equation is not balanced: there are uvo oxygen atoms on the left, but only one on the rightw Step 4. Balance the equation: 2Ptg +02 -• 2t.tgo
  6. Balanced Symbol Equation (contd.) Now work through the steps to find the balanced symbol equation for the reaction that takes place when burning sodium is lowered into a gas jar of chlorine gas. Sodium chloride is produced in this reaction. Remember that chlorine is a cfiatomic gas. We cannot alter the formulae of the substances involved in the reaction. These are formed by the bonding in the substance itself. WE can only put multiplying numbers in front of each formula where necessary alkali metal + water metal hydroxide + hydrogen Therefore: potassium + water potassium hydroxide + hydrogen K + H20 — KOH + H2 An even number of hydrogen atoms is needed on product side, because on reactant side the hydrogen occurs as H20 2K + 2+420 -s 2KOH + H2
  7. 1 2 3 Practice Questions Write word equations fir the reactions described in a—c. a Iron rusts because it reacts with oxygen in the air to form a compound called iron(lll) oxide, b Sodium hydroxide neutralises sulfuric acid to form sodium sulfate and water. c reacts strongly with water to give a solution of eodtum hydroxide; hydrogen gas Is also gtven off. Balance the following symbol equations: cu + 02 _cuo d Na0H + H2S04 -4 NazS04 + _ H 20 Fe + H 20 _ Fe304 + Change these •rd equations into balanced symbol equations. a b c hydrogen * chlorine hydrogen chloride copper + oxygen —e copper oxide may-.esium + zinc chloride magnesium chloride + zinc
  8. State Symbols Symbols used to show the chemical reaction Meanin solid liquid physical state of reactants and products in aq aqueous solution (dissolved in water) Table 4.5: State symbols used in chemical equations.
  9. State Symbols (contd.) For Example: A B C magnesium + nitric acid magnesium nitrate + hydrogen mg(s) + 2HN03(aÄ) + H2(g) hydroChlOric acid + sodium hydroxide sodium chloride + water HCl(aq) + NaoH(aq) — NaC1(aq) + H20(1) copper(ll) sulfate + sodium hydroxide copper(ll) hydroxide + sodium sulfate cuS04(aq) + 2NaoH(aq) + NaS04(aq)
  10. Ionic Equations • Some of the ions present in a chemical reaction are simply spectator ions to the change. These spectator ions are present in a chemical reaction but do not take part in it HC1(aq) + NaoH(Sq) NäC1(aq) * Ha0()) Writing out all the ions present, we get: The use of state symbols clearly show which ions have not changed
  11. Ionic Equations (contd.) Ionic equation of neutralization reaction will be: H+(aq) + OH-(aq) -e Hz0(1) The simplified equation of a reaction involving ionic substances: only those ions which actually take part in the reaction are shown. 4-15: A in which tm «ntalnlng md b; with the sputator 'h o "n.
  12. Ionic Equations (contd.) Write the ionic equation of following chemical reaction cuS04(aq) + 2NaOH(aq) + Na+04(aq) Questions 4 5 6 Explain the meaning of the symbols (s), (aq) and (g) In the following equation, wtth reference to each reactant and product; nazcos(s) + 2HCl(aq) 2UäCl(aq) + H20(l) + coz(g) Wrke an Ionic equation, Including state symbols, for each of the following reactions: a silver nitratesolution + sodium chloride solutlon sover Chloride + sodlurn nitrate solutton b sodium sulfate solution + barium nitrate solution sodium nitrate solution + barium sulfate WI-te fill] syn%ol equations far the following reactions, followed by the ionic equation for the reaction (include state symbols in both types of equaüon). a hydrochloric + potassium hydroxide solution potassium Chloride solution + water b dilute hydrochloric acid + copper carbonate -s copper chloride solution + water + carbon dioxide