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Reactions

Reactions. Chapter 8. Chemical Reaction Equations. A reaction equation must… Represent all known facts Contain correct formulas for reactants and products Follow the law of conservation of mass. Reactants/Products. Reactants are the substances present when the reaction starts.

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Reactions

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  1. Reactions Chapter 8

  2. Chemical Reaction Equations • A reaction equation must… • Represent all known facts • Contain correct formulas for reactants and products • Follow the law of conservation of mass.

  3. Reactants/Products • Reactants are the substances present when the reaction starts. • Products are the substances formed after the reaction takes place.

  4. Writing Equations • Given a word equation you can write a formula equation. • This is done by… • Determining the reactants and products • Writing the correct formula for them • Balancing the reaction.

  5. Equation Symbols • An arrow is used in a formula equation to represent the change from reactants to products. Arrows always point to the products. • Any conditions under which the reaction takes place are written above the arrow. • A reversible reaction that can proceed in both directions is shown using a double arrows. • The phases of the products can be shown in parenthesis as a subscript after the substance. Common phases are (s) solid, (l) liquid, (g) gas, and (aq) aqueous.

  6. Types of Reactions • There are many ways to classify chemical reactions. • One way breaks the reactions down into five basic types: • Synthesis • Decomposition • Single displacement • Double displacement • Combustion

  7. Synthesis • In a synthesis reaction, two or more substances combine to form a new compound. • A + X  AX

  8. The copper Statue of Liberty reacting with oxygen to form the green copper oxide. 2Cu + O2-->    2CuO Iron metal reacts with oxygen to form iron III oxide (rust). 4Fe + 3O2--> 2Fe2O3 Sodium metal reacts with chlorine gas to form sodium chloride (table salt). 2Na + Cl2--> 2NaCl

  9. Decomposition • In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances. • AX  A + X

  10. Carbonic acid decomposes to form water and carbon dioxide. H2CO3--> H2O + CO2

  11. Single Displacement • In a single displacement reaction, one lone cation replaces a cation within a compound. • A + BX  B + AX

  12. Copper wire reacts with silver nitrate solution to form silver and copper nitrate solution Cu + 2AgNO3--> Cu(NO3)2 + 2Ag 2Na + 2HOH --> 2NaOH + H2 *Can form precipitates

  13. Activity Series • To determine whether a single cation has the ability to replace another in a compound depends on the activity series. • This shows the ease with which the elements undergo change in a reaction. • An element can replace any element that falls below it on the activity series. • If the element it is trying to replace is above it on the chart, it will not be able to replace it and no reaction will occur.

  14. Double Displacement • In a double displacement reaction, the cations of two compounds exchange places to form two new compounds. • AX + BY  AY + BX

  15. Magnesium carbonate (an antacid) reacts with hydrochloric acid (found in the stomach) to form magnesium chloride and carbonic acid MgCO3 + 2HCl --> MgCl2 + H2CO3 *Can form precipitates

  16. Combustion • In a combustion reaction, a substance combines with oxygen gas to produce a large amount of energy in the form of heat and light. • Hydrocarbons burn completely in oxygen to produce carbon dioxide and water vapor.

  17. Predicting Products • Given the reactants and the type of reaction, the products of the reaction can be predicted. • To do so, the elements must rearrange in the appropriate way and the correct formulas for the new compounds must be written.

  18. Balancing • To balance you must begin by counting the number of atoms of each element present on the reactant side and product side. • Coefficients must be added that balance the number of atoms of the element. • Coefficients not only change the one element by also any other element within the compound.

  19. Balancing Hints • Write a list of the elements below the reaction with the number that exist. • Cross out these numbers and change them accordingly as you go. • Start with the elements that only appear once on both sides of the equation. • Polyatomic ions are balanced as single units, not as separate elements. • Save hydrogen and oxygen to be balanced last. • Count atoms one last time to ensure everything is equal.

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