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Chemical Change - Reactions - PowerPoint PPT Presentation

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Chemical Change - Reactions
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  1. Chemical Change - Reactions Objectives: At the end of this section you should be able to:- • Explain the difference between chemical and physical change. • Use the periodic table to determine valency. • Explain the significance of the law of constant composition for writing chemical reactions.*** (comeback to) • Write and balance chemical formulae. • Calculate reacting masses for given reactions. • Explain energy changes in reactions. • Explain Avogadro’s law. • Work out reacting volumes of gases.

  2. Chemical Change - Reactions Objectives: At the end of this section you should be able to:- • Distinguish between synthesis and decomposition reactions • Discuss how energy released by chemical reactions is essential for life • Describe how metals react with oxygen • Explain the reverse process in which metals are separated from their oxides • Describe the reactions of non-metals with oxygen • Write balanced equations for reactions involving non-metals.

  3. Physical and chemical change

  4. Physical and chemical change

  5. S SO2 S H2S Formulae CO2 CH4 Elements on the LEFT of the periodic table are written FIRST. If elements are above/below each other then the LOWER one is written FIRST. H O C S S

  6. Constant composition Consider the following analysis of different samples of table salt, what do you notice? Hint??

  7. Constant composition Consider the following analysis of different samples of table salt, what do you notice? Hint?? Ratios??

  8. Constant composition When elements combine with each other to form compounds, they always combine in an exact ratio and mass with one another. Consider the following analysis of different samples of table salt:

  9. The Law of Constant Composition The Law states: A certain chemical compound always contains the ……………………. chemically combined in the ………… …………………….. by …………………….. NaCl CaCl2 KMnO4 K2Cr2O7 Ratios: ……. ……….. ………. ……………. These ratios ………………. change. NaCl is always 1:1 and 23g:35,5g – irrespective of whether the NaCl comes from the UK, USA or SA.

  10. The Law of Constant Composition The Law states: A certain chemical compound always contains the same elements chemically combined in the same proportions by mass. NaCl CaCl2 KMnO4 K2Cr2O7 Ratios: 1:1 1:2 1:1:4 2:2:7 These ratios never change. NaCl is always 1:1 and 23g:35,5g – irrespective of whether the NaCl comes from the UK, USA or SA.

  11. Molecules c b a CO2 O2 3CH4 H2S Methane + oxygen --> water + carbon dioxide CH4 + 2O2 ---> CO2 + 2H2O

  12. Conservation of Mass, Atoms & Molecules Show that mass, atoms are conserved but molecules are not H2 + O2 H2O

  13. REACTIONS Hydrogen and oxygen react to produce water. H2 + O2 H2O Ar: Mr: Balanced Eqn: H2 + O2 H2O LHS: RHS: LHS = RHS MASS is CONSERVED!! This is true for ALL REACTIONS. This is the reaction used to power the space shuttle.

  14. REACTIONS Hydrogen and oxygen react to produce water. (Synthesis reaction) H2 + O2 H2O Ar: H = 1, O = 16 Mr: H2 =2, O2 = 32 H2O = 16+2=18 Balanced Eqn: 2H2 + O2 2H2O LHS: RHS: 2(2) + 32 = 36 2(2+16) = 36 LHS = RHS MASS is CONSERVED!! This is true for ALL REACTIONS. This is the reaction used to power the space shuttle.

  15. 2 1 REACTIONS • Butane reacts with oxygen 2. Carbon dioxide and water are formed Butane + Oxygen ---> Carbon dioxide + water C4H10 + O2 ---> CO2 + H2O What mass of carbon dioxide is produced from each butane molecule?

  16. REACTIONS 2 1 • Butane reacts with oxygen 2. Carbon dioxide and water are formed Butane + Oxygen ---> Carbon dioxide + water 2C4H10 + 13O2 ---> 8CO2 + 10H2O BALANCED! Reaction equation

  17. Reacting Masses Calculate the mass of each underlined compound either produced or required. (Balance the reactions first) • Na + Cl2 --> NaCl • C + Cl2 --> CCl4 • ZnS + O2 --> ZnO + SO2 • FeS + HCl --> H2S + FeCl2 • SO2 + H2S --> S + H2O

  18. Volume - Volume Calculations H2 + N2 --> NH3 If 3.00 dm3 of nitrogen are reacted to produce ammonia, what volume of hydrogen will be required? (At STP)

  19. Volume - Volume Calculations H2 + N2 --> NH3 If 3.00 dm3 of nitrogen are reacted to produce ammonia, what volume of hydrogen will be required? (At STP) • 3H2 + N2 --> 2NH3 • n(N2) = v/Mv = 3/22.4 = 0.134mol • N2 : H2 1:3 n(H2) = 3(N2) • n(H2) = 3(0.13) = 0.401mol • v(H2) = n(H2)Mv = 0.401(22.4) = 8.98dm3

  20. Balancing Reactions • 2Na + Cl2 --> 2NaCl 2NaCl: 2(23+35.5) = 2(58.5)=117g • C + 2Cl2 --> CCl4 CCl4: 12 + 4(35.5) = 154g • 2ZnS + 3O2 --> 2ZnO + 2SO2 SO2: 2(32 + 2(16)) = 128g • FeS + 2HCl --> H2S + FeCl2 FeS: 56 + 32 = 88g • SO2 + 2H2S --> 3S + 2H2O H2S: 2(2 + 32) = 68g

  21. Balancing More Reactions • Na + H2O --> NaOH + H2 • H2 + O2 --> H2O • CaCO3 --> CaO + CO2 • CaCl2 + Na2SO4 --> CaSO4 + NaCl • Al(NO3)3 + K2CO3 --> Al2(CO3)3 + KNO3 • Na3PO4 + MgI2 --> Mg3(PO4)2 + NaI

  22. Balancing More Reactions • 2Na + 2H2O --> 2NaOH + H2 • 2H2 + O2 --> 2H2O • CaCO3 --> CaO + CO2 • CaCl2 + Na2SO4 --> CaSO4 + 2NaCl • 2Al(NO3)3 + 3K2CO3 --> Al2(CO3)3 + 6KNO3 • 2Na3PO4 + 3MgI2 --> Mg3(PO4)2 + 6NaI

  23. BALANCING REACTIONS 2 1 butane • Butane reacts with oxygen 2. Carbon dioxide and water are formed