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Reactions. Five Main Types of Reactions Single Replacement Double Replacement Synthesis Decomposition Combustion h?v=tE4668aarck&safety_mod.

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Presentation on theme: "Reactions. Five Main Types of Reactions Single Replacement Double Replacement Synthesis Decomposition Combustion h?v=tE4668aarck&safety_mod."— Presentation transcript:

1 Reactions

2 Five Main Types of Reactions Single Replacement Double Replacement Synthesis Decomposition Combustion h?v=tE4668aarck&safety_mod e=true&persist_safety_mode= 1&safe=active h?v=tE4668aarck&safety_mod e=true&persist_safety_mode= 1&safe=active

3 Single Replacement A + BX AX + B A and B are cations and X is an anion. The cations exchange position.

4 Double Replacement AX + BY AY + BX A and B are cations & X and Y are anions. Cations trade anions to form two new products. Colorless solutions of lead (II) nitrate and potassium iodide react to produce the yellow precipitate lead (II) iodide and the colorless solution of potassium nitrate.

5 Synthesis A + X AX Elements react to form molecule. Also molecules react to form larger molecules. mWA&safety_mode=true&persist_safety_mo de=1&safe=active mWA&safety_mode=true&persist_safety_mo de=1&safe=active

6 Decomposition AX A + X Molecule breaks apart into smaller products, elements.

7 Combustion C n H 2n O + O 2 CO 2 + H 2 O Reaction of organic molecule containing carbon and hydrogen with oxygen. Products are carbon dioxide and water.

8 Writing Reaction Equations Write a sentence describing the reaction that includes the names and states of all reactants and products, and any special conditions the reaction requires. – "Ozone gas decomposes into oxygen gas when exposed to ultraviolet light.

9 Add symbols Separate reactants & products with a process symbol: – reaction goes to completion; – sometimes used for one-step reactions reaction is reversible; at equilibrium, reactants and products are mixed – = net reaction; reaction occurs in several steps. – Catalysts are usually written on top of the process symbol. Ozone gas oxygen gas

10 Replace names with formulas Replace names with formulas; put plus signs between formulas. O 3 (gas) O 2 (gas)

11 Add symbols for phase state Include symbols for physical states: – (g) gas – (l) liquid – (s) solid – (aq) aqueous (dissolved in water) O 3 (g) O 2 (g)

12 Balance atoms and charges "Balance" the equation by adding coefficients so atoms and charge are conserved. Each side of a balanced equation must have: – the same number of atoms of each type – the same total charge 2 O 3 (g) 3 O 2 (g)

13 Law of Conservation of Mass Lavoisiers quantified research into combustion showed the mass of hydrogen and oxygen reactants equals the mass of H 2 O produced. Mass is neither created nor destroyed in chemical reactions. This law requires that reaction equations balance, every atom accounted for.

14 Balancing Equations Elements are included in equations in the form that they exist in nature: diatomic gases, Hg Most elements exist as single atoms for the simplest form. The number and kind of atoms on each side of the reaction arrow are the same, and therefore the equation is balanced. Formula units (atom, ion, or molecule) must be identified for each substance that participates in the reaction.

15 Process for balancing Write the formulas for the reactant(s) and product(s). Find suitable coefficients for each substance. Reduce the coefficients to their smallest whole number values. – Divide by a common divisor if necessary. Check your work to be sure the number and type of atom is the same on both sides of equation.

16 Coefficients Strategystart with most complex molecule. – Balance for each kind of atom in the molecule, one at a time. KClO 3 + C 12 H 22 O 11 KCl + CO 2 + H 2 O 1.C 2.H 3.O 4.K 5.Cl 12 Start with C in largest molecule, 12 on the left. Multiply CO 2 by 12. Next H, 22 on the left. Multiply H 2 O by Next O, on the left, and on the right Left side needs 21 more. Multiply KClO 3 by 8 (It has 3 Os plus 7*3 Os needed = 8 coefficient. Next K, 8 on the left. Multiply KCl by 8. Next Cl, 8 on the left. Have 8 on the right. 88

17 Try these? C 6 H 12 O 6 C 2 H 6 O + CO 2 fermentation of sugar to yield alcohol. Fe + O 2 Fe 2 O 3 rusting of iron. NH 3 + Cl 2 N 2 H 4 + NH 4 Cl synthesis of hydrazine for rocket fuel. KClO 3 KCl + O 2 decomposition reaction used to produce oxygen for the emergency breathing masks in airliners. 22 Start with sugar on left. Balance carbon(remember to add up all C), then oxygen. Start with iron (III) oxide. Add 2 in front of iron. LCM for O is 6. Add 3 to O 2 and 2 in front of Fe. Recheck the tally. Left has 2 Fe and right side has 4. Adjust left side Fe to Start with ammonium chloride on right. Balance chlorine; multiply left by 4.. Balance N(remember to add up all CN), then hydrogen. Start with potassium chlorate on left. Balance oxygen; find least common multiple for oxygen on both sides. Multiply left side KClO 3 by 2 and the right O 2 by 3. Balance potassium, and multiply right side by

18 Predicting reactions A world of watermany reactions occur in aqueous solutions. Precipitation reactionsproceed in the direction of a stable precipitate formation as the ions are removed from the solution. – Common for single or double replacement reactions. Pb(NO 3 ) 2(aq) + 2KI (aq) 2KNO 3(aq) + PbI 2(s)

19 Predicting reactions Acid-base neutralization reactions are processes in which an acid(H + ) & a base(OH-) react to yield water and a salt (ionic compound) – Double replacement reaction HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) The driving force behind the neutralization reaction is the production of the stable covalent water molecule by removing the H + and OH- out of solution.

20 Predicting reactions Oxidation-reduction or redox reactionsare processes in which one or more electrons are transferred between reaction partners. – Common to synthesis or decomposition reactions. Mg (s) + I 2(g) MgI 2(s) The driving force is the reduction in electrical potential (analogous to what happens when a live electrical wire is grounded and electrons flow from the wire to the ground.) Charges on the atoms change.

21 Activity Series Li K Ba Ca Na Mg Al Mn Zn Cr Fe Co Ni Sn H 2 Cu Ag Hg Pt Au These elements react rapidly with aqueous H+ ions (acid) or with liquid H 2 O to release H 2 gas. These elements react with aqueous H+ ions or with steam to release H 2 gas. These elements react with aqueous H+ ions to release H 2 gas. These elements do not react with aqueous H+ ions to release H 2. More reactive Strongly reducing

22 Significance of Equations On a microscopic level, the equation describes the behavior of individual atoms and molecules. On a macroscopic level, formulas and equations represent the large scale behaviors of atoms and molecules that give rise to visible properties. – The symbols represent vast numbers of molecules that together have measurable physical properties. Example: a single H 2 O molecule is neither solid, liquid, nor gas. A huge collection of H 2 O molecules appears as a colorless liquid that freezes at 0 o C.

23 Resources 1/reactions/index.shtml notes-equations 1/reactions/index.shtml 1/compounds/index.shtml notes-ions 1/compounds/index.shtml cing-chemical-equations java based game cing-chemical-equations

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