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© University of South Carolina Board of Trustees Chapt. 18 Electrochemistry Sec. 2 Balancing Redox Reactions
© University of South Carolina Board of Trustees Balancing Redox Reactions Copper dissolves in nitric acid to form Cu 2+. NO (g) is released at the same time. Find the balanced chemical equation. aCu (s) + bNO 3 − (aq) + cH + (aq) dCu 2+ (aq) + eNO (g) + fH 2 O (l)
© University of South Carolina Board of Trustees Balancing Redox Reactions Acid Solution 1.Assign oxidation states. 2.Identify reduction and oxidation half-reactions. aCu (s) + bNO 3 − (aq) + cH + (aq) dCu 2+ (aq) + eNO (g) + fH 2 O (l)
© University of South Carolina Board of Trustees Half-Reactions 2a.Write the reduction and oxidation portions of the reaction separately. oxidation states 2b.Use e − to balance oxidation states in each half-reaction. ●e − will cancel out in full reaction
© University of South Carolina Board of Trustees Balancing Redox Reactions Acid Solution 1.Assign oxidation states. 2.Identify reduction and oxidation half-reactions. 3.Balance the electrons, then balance atoms except H and O. 4.Combine half-reactions so no free e − appear. 7.Double check charge balance. 6.Add H + to balance H. 5.Add H 2 O to balance the O.
© University of South Carolina Board of Trustees Student Example Balance the equation (acid solution) Cr 2 O 7 2− + C 2 H 5 OH Cr 3+ + CO 2
© University of South Carolina Board of Trustees Balance the equation Cu (s) + NO 3 - (aq) Cu 2+ (aq) + NO (g) if the reaction occurs in basic solution (H 2 O and OH − readily available) Balancing Redox Reactions Basic Solution
© University of South Carolina Board of Trustees Balance the equation Cu (s) + NO 3 - (aq) Cu 2+ (aq) + NO (g) if the reaction occurs in basic solution (H 2 O and OH − readily available) 1.Solve the problem in acidic solution. Balancing Redox Reactions Basic Solution
© University of South Carolina Board of Trustees Balance the equation Cu (s) + NO 3 - (aq) Cu 2+ (aq) + NO (g) if the reaction occurs in basic solution (H 2 O and OH − readily available) 1.Solve the problem in acidic solution. 2.Add OH - to each side to eliminate H +. Balancing Redox Reactions Basic Solution
© University of South Carolina Board of Trustees Balance the equation Cu (s) + NO 3 - (aq) Cu 2+ (aq) + NO (g) if the reaction occurs in basic solution (H 2 O and OH − readily available) 1.Solve the problem in acidic solution. 2.Add OH − to each side to eliminate H Cancel extra H 2 O formed. Balancing Redox Reactions Basic Solution
© University of South Carolina Board of Trustees Student Example Balance the reaction Zn + ClO − Zn(OH) 4 2− + Cl − in basic solution.
© University of South Carolina Board of Trustees Final Example When O 2 and H 2 are present in reaction they are involved in the redox chemistry Ag + CN - + O 2 Ag(CN) 2 - In this case you must add H 2 O to the reaction. Ag + CN - + O 2 Ag(CN) H 2 O Similar with H 2 H 2 + Pt + Pt Must add H+ to reaction to be able to solve H 2 + Pt + Pt + 2H +
Half-reactions show the oxidation or reduction reaction separated. Cu (s) + 2 AgNO 3(aq) → Cu(NO 3 ) 2(aq) + 2 Ag (s) Oxidation:Cu → Cu e – Reduction:Ag.
+ Redox Reactions. + Oxidation Reduction (REDOX) Reactions Reactions in which one or more electrons are transferred (redox reactions) Example: H 2(g)
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Balancing Redox Reactions. Half Reaction Method 1.Write the formula equation if it is not given. Then write the ionic equation. Formula eq: H 2 S + HNO.
Electrochemistry Chapter 5. 2Mg (s) + O 2 (g) 2MgO (s) 2Mg 2Mg e - O 2 + 4e - 2O 2- Oxidation half-reaction (lose e - ) Reduction half-reaction.
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Chapter 20 – Redox Reactions One of the earliest recognized chemical reactions were with oxygen. Some substances would combine with oxygen, and some would.
Balancing Redox Equations. In balancing redox equations, the # of electrons lost in oxidation (the increase in ox. #) must equal the # of electrons gained.
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Ammonium Dichromate Volcano! 1)When heated, ammonium dichromate decomposes to produce a chromium oxide compound, a gas, and water vapor. Write and balance.
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Redox Reactions Atom 1 Atom 2 Gives electrons This atom Oxidizes itself (loses electrons) It’s the reducing agent This atom Reduces itself (gains electrons)
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Balancing Oxidation Reduction Equations. Oxidation and Reduction Oxidation – the atom loses electrons –The charge becomes more positive Reduction – the.
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