Lectures: Balancing chemical reactions - PowerPoint Presentation

1. Lectures:Balancing chemical reactionsChemical Quantities and reactions Course lecturer : Dr. Altijana Hromić-Jahjefendić

2. 1 mole of an element = 6.02 x 1023 atoms of that element

3. Moles of Elements in a Chemical FormulaSubscripts – indicate the number of atoms of each type of element in the compoundExample: aspirin (C9H8O4) has 9 carbon atoms, 8 hydrogen atoms and 4 oxygen atomsAlso tells the number of moles of each element in 1 mole of aspirin9 moles of C atoms, 8 moles of H atoms and 4 moles of O atoms

4. Moles and Elements in a given formula

5. Molar Mass and CalculationsSingle atom or molecule is too small to weighIt takes a huge number of atoms or molecules to make enough of a substance for you to seeMolar mass – quantity in grams that equals the atomic mass of that elementExample: carbon has atomic mass of 12.011 mole of carbon atoms has a mass of 12.01 gTo obtain 1 mole of carbon atoms we must weigh out 12.01 g of carbon

6. Calculation of true massM=m/nMolar mass=mass/molesTo weight the compound

7. Equations for Chemical ReactionsChemical change – when a substance is converted into one or more new substances (different formulas and properties)Example: the tarnishing of silverShiny silver metal (Ag) reacts with sulfur (S) Becomes dull, black substance we know as tarnish (Ag2S)

8. Chemical reaction – involves chemical change Atoms of the reacting substances form new combinations with new propertiesExample: chemical reaction of iron (Fe) with oxygen (O2) in the airProduce a new substance Fe2O3 (rust; reddish-brown color)During chemical change new properties become visible – indicates that a chemical reaction has taken place

9. Writing a Chemical EquationChemical reaction represented by chemical equationExample: burning charcoal in a grillCombines with oxygen to form CO2

10. In chemical equation – reactants and productsReactants are written on the left of the arrow and products on the rightIf there are two or more formulas on the same side they are separated by plus (+) signsEach formula is followed by physical state of the substance: solid (s), liquid (l) or gas (g).If the substance is dissolved in water it is aqueous (aq) solution

11. Identifying a Balanced Chemical EquationIn chemical reaction bonds between atoms of the reactants are broken New bonds are formed to give the productsAll atoms are conserved – atoms cannot be gained, lost or changed into other types of atoms during a chemical reactionEvery chemical reaction must be written as a balanced equationSame number of atoms for each element in the reactants as well as in products!!!!!!!!

12. Balancing of Chemical ReactionsIn the balanced equation there are whole numbers called coefficients in front of the formulas H2 + O2  H2O - unbalanced 2H2 + O2  2H2O - balanced

13. This illustrates the Law of Conservation of Matter, which states that matter cannot be created or destroyed during a chemical reaction.

14. Types of ReactionA great number of reactions occur in nature There are some general patterns of classification

15. CombinationIn a combination reaction, two or more elements or compounds bond to form one product.Example: sulfur and oxygen combine to form the product sulfur dioxide.

16. Examples

17. Decomposition ReactionsIn a decomposition reaction, a reactant splits into two or more simpler products. For example, when mercury (II) oxide is heated, the compound breaks apart into mercury atoms and oxygen 2HgO  2Hg + O2

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19. Replacement ReactionsIn a replacement reaction, elements in a compound are replaced by other elements. Single replacement reaction - reacting element switches place with an element in the other reacting compound

20. In a double replacement reaction - positive ions in the reacting compounds switch places.

21. Combustion reactionsA carbon-containing compound (fuel) burns in oxygen from the air to produce CO2, water or energy in the form of heat or flameExamples: Burning of a candle or fuel

22. Link to HealthToxicity of carbon monoxide – incomplete combustionPropane heater in a closed room – proper ventilatonIf supply of oxygen is limited – incomplete combustion from burning gas,oil or wood produces CO

23. Link to HealthCO (carbon monoxide) is a colorless, odorless and poisonous gasIf inhaled, passes into the bloodstreamAttaches to hemoglobin which reduces the amount of oxygen (O2) reaching the cellsResult: person can experience a reduction in exercise capability, visual perception and other disorders

24. Link to HealthHemoglobin is the protein that transports O2 in the bloodIf amount of hemoglobin bound to CO is about 10% - shortness of breath, mild headache and drowsinessHeavy smokers can have up to 9%If the amount is 30% - dizziness, mental confusion, severe headacheIf amount is 50% or more – person could become uncounscious and die if not treated immediatelly with oxygen

25. Oxidation-Reduction reactionsIn everyday lifeRusting (Fe is oxidized)Turning lights in our cars (car battery provides electicity)Burning woods Combustion reactions are also oxidation-reduction reaction

26. Also called redox reactionsElectrons are transferred from one substance to anotherOne substance loses electrons, another one gains electronsOxidation – loss of electronsReduction – gain of electrons

27. Atoms of metals lose electrons to form positive ions – metals are oxidizedNonmetals gain electrons to form negative ions – nonmetals are reduced

28. Oxidation and Reduction in Biological SystemsIn the body cellsOxidation of organic carbon compounds involves the transfer of hydrogen atoms (protons and electrons)Necessary for the production of energy in the cellsHowever, redox reactions depend on the process that occursBut oxidation is always loss of electronsReduction is always gain of electrons

29. Balancing of chemical reactionsH2 + O2 → H2OS + O2 → SO2Mg + O2 → MgOMgO + CO2 → MgCO3N2 + H2 → NH3HgO → Hg + O2Zn + HCl → H2 + ZnCl2NaOH + HCl → H2O + NaClC6H12O6 + O2 → CO2 + H2O + energyFe2S3 + HCl → FeCl3 + H2SCH4 + O2 → CO2 + H2O

30. Balancing of chemical reactionsNa3PO4 + MgCl2 → Mg3(PO4)2 + NaClAl + CuSO4 → Al2(SO4)3 + CuK2SO4 + BaCl2 → KCl + BaSO4Sb2S3 + HCl → SbCl3 + H2SZn + HNO3 → Zn(NO3)2 + H2C2H4 + O2 → CO2 + H2O + energyAgNO3 + K2CrO4 → Ag2CrO4 + KNO3Ba(OH)2 + H3PO4 → Ba3(PO4)2 + H2OH3PO4 + NaOH → Na3PO4 + H2OFeCl3 + NH4OH → Fe(OH)3 + NH4Cl

31. SummaryMolar mass and calculationsChemical reactionsBalancing of chemical reactions

32. Mole relationships in Chemical EquationsIn any chemical reaction, the total amount of matter in the reactants is equal to the total amount of matter in the products.Thus, the total mass of all the reactants must be equal to the total mass of all the productsKnown as the law of conservation of mass, which states that there is no change in the total mass of the substances reacting in a chemical reaction.

33. Example: tarnish (Ag2S) forms when silver reacts with sulfur from silver sulfideIn this reaction the number of silver atoms is twice the number of sulfur atoms

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35. Energy in Chemical ReactionsMolecules of the reactants must collide with each other, have proper orientation and energySufficient energy to break the bonds of the reactantsActivation energy – amount of energy required to break the bonds between atoms

36. Energy in Chemical ReactionsThree Conditions Required for a Reaction to Occur1. Collision - The reactants must collide.2. Orientation - The reactants must align properly to break and form bonds.3. Energy - The collision must provide the energy of activation.

37. Exothermic ReactionsHeat is absorbed or released as reactants convert to the productsIn exothermic reaction – energy of the products is lower that the energy of the reactantsHeat is released in exothermic reactions

38. Endothermic reactionsThe energy of the products is higher than of the reactantsHeat is absorbed in endothermic reactions

39. Chemistry Link to HealthFirst-aid station: cold packReduces swelling from an injury, removes heat from inflammationInside of cold pack is solid ammonium nitrate separated from the compartment containig waterActivation: hiting or squeezing to break the walls and mix nitrate with water

40. Chemistry to HealthHot packs Contain salt CaCl2When 1 mole of CaCl2 dissolves in water, energy is released as heatThe temperature rises to almost 66 °C and can be used

41. Rate of ReactionThe rate (speed) is measured by:- the amount of reactant used up- the amount of product formedIn a certain period of timeThe rate is affected by:Changes in temperatureChanges in the concentration of the reactantsAddition of catalysts

42. TemperatureHigher temperatures – increase in kinetic energy makes reactants move faster and collide oftenHigher temperatures – faster reactionsExample: cookingLower temperatures – slower reactionsExample: in cardiac surgery, body temperature is lowered to 28 °C so the heart can be stopped and less oxygen is required by the brainThe reason why some people survived submersion in icy lakes for longer period

43. Concentrations of ReactantsAdding reactants – increasing the rate of reactionMore collisions between the reactants -> reaction fasterExample: patient with difficulty breathing may be given a mixture with a higher oxygen contantThe increase in the number of oxygen molecules in the lungs – increases the rate at which oxygen combines with hemoglobin

44. CatalystsTo speed up a reaction – lower the energy of activationAdding catalystProvides alternate pathway with a lower energy requirenmentResult: more collisions form product successfullyMany uses in industry (margarine production speed up with platinum)In body – enzymesMake most metabolic reactions go at the rates needed for proper cellular activity

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46. SummaryTypes of reactionsRedox reactionsMole relationships in chemical equationsMass calculations for reactionsEnergy in chemical reactionsRate of reactions

47. Assignment Calculate the the mass in grams for following compounds:1.75 moles of C19H20FNO34.42 moles of C4H8O42 moles of Ga2(CO3)25 moles of Al2(SO4)30.5 moles of Mg(OH)23.75 moles of Fe2O3M=m/n