Please show work and answer in readable handwriting, thanks. Do questions based on the table of reduction potentials.
Posted: Mon May 16, 2022 11:24 pm
Please show work and answer in readable handwriting, thanks. Do
questions based on the table of reduction potentials.
sty S MacBook Ait ENERGY FOR REDOX REACTIONS Predicting the Direction of a Reaction Goals: 1. To determine which reactants will combine to give a spontaneous reaction; 2. To apply the pattern/method from (1) to predict whether a given reaction will be spontaneous. Introduction Redox Reactions Oxidation-Reduction /Redox reactions are called electron-transfer reactions. These reactions are generally studied by dividing the reaction process into two steps, called half-reactions (the sum of which gives the overall reaction) as shown in the following example. The overall reaction is conducted by mixing two reactants in a test tube, Mg metal and 1 ml of 0.1 M CuCl2 val. The overall reaction is: Mgs + Culea ) Cu aj + Mga The two half reactions are: Mg(s) —> Mg 2 (aq) + 2 e- "? oxidation (decrease in electrons)/anode Cut? (aq) + 2 e--> Cu (s) reduction (increase in electrons)/cathode In this reaction the Mg (s) is said to be oxidized (has a greater tendency to give up electrons) and the Cut? is reduced (has a greater tendency to gain electrons compared to Mg(s)). [For the reactions in this experiment, the anion of the ionic compound is not part of the reaction.] The information is generally presented in a table of half-reactions, with energy values in units of volts, V) for the relative tendency of each species to gain electrons (be reduced/undergo reduction); several half-reactions are presented below: Table of Reduction Potentials E Ag+ (aq) +1 e- -> Ag (s) +0.80 V Cu? (aq) + 2 e- -> Cu (s) +0.34 V 2 Haq) +2 e- > H, (8) 0.00 V Zn (aq) + 2e -> Zn (s) -0.76 V Al(aq) + 3 e--> Al (s) -1.66 V Mg"(aq) + 2 e--> Mg(s) -2.36 V "This is a small group of half-reactions selected for this experiment. A more complete table can be found in the textbook or the a Chemical Rubber Handbook of Chemistry and Physics in the lab. 1 Redox Reactions
MacBook Air Note that the BOTH REACTANTS MUST BE written on the left side of the chemical equation. For the example, the Mg(s) reactant is on the right side, and the half reaction was reversed when written as an oxidation The energy for the reaction, Eceil, can be calculated from the energy of each half reaction in the following equation: E cell = Ereduction/cathode. E oxidation/anode (values taken directly from the Table of Reduction Potentials) For the reaction presented above, the calculation is: E cell = (+0.34 V) - (-2.36 V) = + 2.70 V Spontaneity of a Chemical Reaction The general criterion for spontaneity of a reaction is the (sign) value of the free energy for the reaction, AG reaction: If AG reaction <0, the reaction will be spontaneous. For the specific case of the energy in redox reactions, Ecuile the relationship is: AG reaction =-n FECI F = 9.649 x 109 J/V Where n is the number of electrons needed in order to balance the reaction with the two half-reactions, and F is the Faraday constant. From this equation, specifically for a redox reaction, the relationship becomes: E cel > 0, for a spontaneous reaction For the example above, where the calculated El= + 2.70 V, the reaction is spontaneous. The Equilibrium Constant and Ecell The equilibrium constant of a redox reaction, K, is related to Ecel by the following equation: Ec= (0.0592 V) log K n Ecell or as, log K = n 0.0592 v Note: The values for Kin redox reactions will generally be VERY large, e.g., 1 x 10*150, which means that the reactions occur as entirely product-favored (100% reaction)! For the example above, AG = -(2) (9.649 x 10^I/V) (+ 2.70 V) = -5.21 x 10) = -521 kJ log K = (2+2.70 V) = + 91.2 0.0592 V so K = 1091.2 = 1.6 x 10*1 !!!! 2 Redox Reactions
BO FI Writing and Balancing the Chemical Equation Using Half-Reactions 1. Identify the half-reaction for each reactant. NB: A reactant could be on either the left OR the right side of the half reaction, as presented in the Table of reduction Potentials. 2. Remember that the two reactants of any chemical reaction must both be on the LEFT side of the chemical equation for that reaction. So, If a reactant is on the right side of the half-reaction in the Table, then that half reaction would have to be written in the reverse direction (making it an oxidation, rather than a reduction step). In the example on page 1, the Mg(s) is on the right side of the half reaction in the Table and its half-reaction reversed to place the Mg(s) on the left side as a reactant. 3. To write the overall reaction, the two half-reactions will be added together. Before that is carried out, the number of electrons for both reactions must also be the same, so that they will cancel in the addition. This may require some algebra to find the common multiple. Example: Reactants: Cu (s) and 0.10M AgNO 1.) Half-reactions used in reactants: Ag ** (aq) +1 e- -> Ag (s) Cut? (aq) + 2 e--> Cu (s) +0.80 V +0.34 V 2.) The Cu(s) is on the right side, so its half-reaction must be reversed - this means that it is the oxidation step. Rewriting the two half reactions: Ag + (aq) + 1 e--> Ag (s) reduction Cu (s) —> Cu2 (aq) + 2e- oxidation 3.) To write the overall chemical equation, we note that there is le- for the reduction and 2 e-for the e- oxidation. The number of electrons must be equal for both half-reactions, so we will multiply the reduction by 2; the equations become +1 2 Ag+ (aq) + 2 e- -> 2 Ag (s) reduction Cu (s) → Cut2 (aq) + 2 e- oxidation 2 Ag (aq) + Cu (s) —> 2 Ag (s) + Cu"? (aq) + ? +1 For the calculation of AG and K, n = 2 because 2 electrons are needed to balance the equation so that the number of electrons will cancel algebraically. (We don't have any "spare" electrons in chemical reactions! Only the physicists can do that!) E cell = E reduction/cathode - E oxidation/anode = +0.80 V - (+0.34 V) = +0.46 V AG reaction = nF Ecell = -(2) (9.649 x 10° /V) (+0.46 V) = - 8.9 x 10*) or -89 kJ log K = n Ecell 0.0592 V (2)(+0.46 V) = 0.0592 V = +16 So K = 1 x 10 ** so This reaction is spontaneous, since E cell and AG reaction <0. 3 | Redox Reactions
dty MacBook Air esc Experimental Procedure PART (1) A. For each reaction, mix the two reactants in a test tube. Use approximately 1 mL of each solution or one piece of metal as specified for the two reactions. Make observations of any visible change (color, bubbling, dissolving of the metal, etc.) that occurs, and record this on the data sheet. Note: Any reaction will occur within 3-4 minutes. B. Identify the half-reaction that is associated with each reactant, and write it on the line provided, including the E value from the table. For each half-reaction, circle the reactant added. Label each half-reaction as either oxidation or reduction. If the reactant is on the left side of the half- reaction, then it is a reduction; if it is on the right side, then it is an oxidation. Calculate the reaction energy. Eccl. If the cell cannot be calculated, then explain why it cannot be C. Determine the pattern of spontaneous reaction between any two reactants. A reaction can be predicted to be spontaneous, based on the relative position of the two reactants in the Table. Look at each reaction which was spontaneous. Take the pair of reactants for each individual reaction and note which side each reactant is on (You could circle them in pencil, for example). Also compare where the reactants are relative to one another in the vertical direction. Which one is higher than the other? Is the reactant on the left side higher than the one on the right? Compare the position of each reactant in the two mixtures that did not react. These are two different cases. For one case, it is because Ecel<0. Describe this case in term of the relative position of the reactants. The overall goal for PART (1) is to determine the pattern of reactivity for any two given reactants - to be able to use the position of each reactant in the Table to conclude whether or not the reaction is spontaneous, without having to write the reaction and calculate Ecell! PART (2) A. For each of the 6 reactions, calculate and record the value of Ecell, or otherwise state why this calculation cannot be done. Determine the overall chemical equation for the reaction and write it on the line provided. Then calculate AG and K for each reaction which has a calculated value for Ecell, including the non-spontaneous reactions as well. From this result, predict which reactions will occur (are spontaneous), and indicate this on the data sheet by circling your response. B. Carry out all 6 reactions, following the instructions from PART (1)(A). Check any calculations again and/or rerun the reaction if the prediction does not agree with the experimental result 4 | Redox Reactions
1 Zatv esc MacBook Air Name Energy for Redox Reactions PART (1) 1. Reactants: magnesium metal, Mg (s), and 0.10 M HCI Observations Half-Reactions: Grayish Cloudy color bubbles, Phizzing Mt2 +2e-my 2H222 _H2 Or hed E° (V) Oxidation or Reduction? -2.360 OX Circle the reactant in each half-reaction. Calculation for Ecell-or explanation why calculation can't be done: -2.76U -> OU=+2.36V Ecoll +2.36v 2. Reactants: copper metal, Cu (s), and 0.10M AgNO. +234 ox Observations Small bubbles removes comer color to Silver color E° (V) "Oxidation or Reduction? Half-Reactions: Cuit+26 -> Cu cu +.80 Red Circle the reactant in each Kalf-reaction. Calculation for Ecellor explanation why calculation can't be done: .80 -.34 ..460 Agti té ->Ag Ecos 460 3. Reactants: copper metal, Cu (s), and 0.10 M HC Observations No heaction E° (V) Oxidation or Reduction? Half-Reactions: Circle the reactant in each half-reaction. Calculation for Ecell-or explanation why calculation can't be done: NO Edell reaction takes place because copper cant replace Hydrogen from Her, because of its low reactivity than hydrogen 5 Redox Reactions
esc sty JO MacBook 80 4. Reactants: 0.10 M Mg(NO), and 0.10 M Cu(NO) Observations_ light blue No bubbling E° (V) Oxidation or Reduction? Half-Reactions: Circle the reactant in each half-reaction. Calculation for Ecell - or explanation why calculation can't be done: Ecell Conclusions 1. What is the general pattern for the relative position of the two reactants for a spontaneous reaction to occur? 2. What are the two cases for a reaction to NOT occur? Describe each case in terms of the relative positions on the table of reduction potentials of the two reactants: Case A Case B PART (2) Note: show calculations as directed by the lab instructor 1. Reactants: copper metal, Cu(s), and 0.10 M Mg(NO3)2 Reaction: V Ecell AG kJ K Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: Took Shommes of copper away, looks dlacker 2. Reactants: zinc metal, Zn (s), and 3M HCl (or 6M) Reaction: use K Ecengles V kJ AG agus Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: Instantly bubbles, Smokey amc Heered black 6 Redox Reactions
MacBook Air will 80 23 2 3. 3. Reactants: 0.10 M Al(NO2)and 0.10 M AgNO, Reaction: Ecell AG kJ K Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: No reaction 4. Reactants: zinc metal, Zn(s) and 0.10 Cu(NO3)2 Reaction: Ecell V AG kJ Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: 2 mc turned black, light blue liquid 5. Reactants: copper metal, Cu (s), and 0.10 M Al(NO), Reaction: V Ecell AG kj K Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: Copper less Shisky, looks darker 6. Reactants: aluminum metal, Al(s), and 3 M HCl (or 6M) Reaction: s Ecoll 6.66 V AG -9,56210² k ko 10 Prediction: Spontaneous / Not Spontaneous (or no reaction) Spontaneous Observations: Bubbles gets bat, smokey creates condensation, final color is greyish/black. 7 | Redox Reactions
questions based on the table of reduction potentials.
- Please Show Work And Answer In Readable Handwriting Thanks Do Questions Based On The Table Of Reduction Potentials 1 (98.07 KiB) Viewed 48 times
MacBook Air Note that the BOTH REACTANTS MUST BE written on the left side of the chemical equation. For the example, the Mg(s) reactant is on the right side, and the half reaction was reversed when written as an oxidation The energy for the reaction, Eceil, can be calculated from the energy of each half reaction in the following equation: E cell = Ereduction/cathode. E oxidation/anode (values taken directly from the Table of Reduction Potentials) For the reaction presented above, the calculation is: E cell = (+0.34 V) - (-2.36 V) = + 2.70 V Spontaneity of a Chemical Reaction The general criterion for spontaneity of a reaction is the (sign) value of the free energy for the reaction, AG reaction: If AG reaction <0, the reaction will be spontaneous. For the specific case of the energy in redox reactions, Ecuile the relationship is: AG reaction =-n FECI F = 9.649 x 109 J/V Where n is the number of electrons needed in order to balance the reaction with the two half-reactions, and F is the Faraday constant. From this equation, specifically for a redox reaction, the relationship becomes: E cel > 0, for a spontaneous reaction For the example above, where the calculated El= + 2.70 V, the reaction is spontaneous. The Equilibrium Constant and Ecell The equilibrium constant of a redox reaction, K, is related to Ecel by the following equation: Ec= (0.0592 V) log K n Ecell or as, log K = n 0.0592 v Note: The values for Kin redox reactions will generally be VERY large, e.g., 1 x 10*150, which means that the reactions occur as entirely product-favored (100% reaction)! For the example above, AG = -(2) (9.649 x 10^I/V) (+ 2.70 V) = -5.21 x 10) = -521 kJ log K = (2+2.70 V) = + 91.2 0.0592 V so K = 1091.2 = 1.6 x 10*1 !!!! 2 Redox Reactions
BO FI Writing and Balancing the Chemical Equation Using Half-Reactions 1. Identify the half-reaction for each reactant. NB: A reactant could be on either the left OR the right side of the half reaction, as presented in the Table of reduction Potentials. 2. Remember that the two reactants of any chemical reaction must both be on the LEFT side of the chemical equation for that reaction. So, If a reactant is on the right side of the half-reaction in the Table, then that half reaction would have to be written in the reverse direction (making it an oxidation, rather than a reduction step). In the example on page 1, the Mg(s) is on the right side of the half reaction in the Table and its half-reaction reversed to place the Mg(s) on the left side as a reactant. 3. To write the overall reaction, the two half-reactions will be added together. Before that is carried out, the number of electrons for both reactions must also be the same, so that they will cancel in the addition. This may require some algebra to find the common multiple. Example: Reactants: Cu (s) and 0.10M AgNO 1.) Half-reactions used in reactants: Ag ** (aq) +1 e- -> Ag (s) Cut? (aq) + 2 e--> Cu (s) +0.80 V +0.34 V 2.) The Cu(s) is on the right side, so its half-reaction must be reversed - this means that it is the oxidation step. Rewriting the two half reactions: Ag + (aq) + 1 e--> Ag (s) reduction Cu (s) —> Cu2 (aq) + 2e- oxidation 3.) To write the overall chemical equation, we note that there is le- for the reduction and 2 e-for the e- oxidation. The number of electrons must be equal for both half-reactions, so we will multiply the reduction by 2; the equations become +1 2 Ag+ (aq) + 2 e- -> 2 Ag (s) reduction Cu (s) → Cut2 (aq) + 2 e- oxidation 2 Ag (aq) + Cu (s) —> 2 Ag (s) + Cu"? (aq) + ? +1 For the calculation of AG and K, n = 2 because 2 electrons are needed to balance the equation so that the number of electrons will cancel algebraically. (We don't have any "spare" electrons in chemical reactions! Only the physicists can do that!) E cell = E reduction/cathode - E oxidation/anode = +0.80 V - (+0.34 V) = +0.46 V AG reaction = nF Ecell = -(2) (9.649 x 10° /V) (+0.46 V) = - 8.9 x 10*) or -89 kJ log K = n Ecell 0.0592 V (2)(+0.46 V) = 0.0592 V = +16 So K = 1 x 10 ** so This reaction is spontaneous, since E cell and AG reaction <0. 3 | Redox Reactions
dty MacBook Air esc Experimental Procedure PART (1) A. For each reaction, mix the two reactants in a test tube. Use approximately 1 mL of each solution or one piece of metal as specified for the two reactions. Make observations of any visible change (color, bubbling, dissolving of the metal, etc.) that occurs, and record this on the data sheet. Note: Any reaction will occur within 3-4 minutes. B. Identify the half-reaction that is associated with each reactant, and write it on the line provided, including the E value from the table. For each half-reaction, circle the reactant added. Label each half-reaction as either oxidation or reduction. If the reactant is on the left side of the half- reaction, then it is a reduction; if it is on the right side, then it is an oxidation. Calculate the reaction energy. Eccl. If the cell cannot be calculated, then explain why it cannot be C. Determine the pattern of spontaneous reaction between any two reactants. A reaction can be predicted to be spontaneous, based on the relative position of the two reactants in the Table. Look at each reaction which was spontaneous. Take the pair of reactants for each individual reaction and note which side each reactant is on (You could circle them in pencil, for example). Also compare where the reactants are relative to one another in the vertical direction. Which one is higher than the other? Is the reactant on the left side higher than the one on the right? Compare the position of each reactant in the two mixtures that did not react. These are two different cases. For one case, it is because Ecel<0. Describe this case in term of the relative position of the reactants. The overall goal for PART (1) is to determine the pattern of reactivity for any two given reactants - to be able to use the position of each reactant in the Table to conclude whether or not the reaction is spontaneous, without having to write the reaction and calculate Ecell! PART (2) A. For each of the 6 reactions, calculate and record the value of Ecell, or otherwise state why this calculation cannot be done. Determine the overall chemical equation for the reaction and write it on the line provided. Then calculate AG and K for each reaction which has a calculated value for Ecell, including the non-spontaneous reactions as well. From this result, predict which reactions will occur (are spontaneous), and indicate this on the data sheet by circling your response. B. Carry out all 6 reactions, following the instructions from PART (1)(A). Check any calculations again and/or rerun the reaction if the prediction does not agree with the experimental result 4 | Redox Reactions
1 Zatv esc MacBook Air Name Energy for Redox Reactions PART (1) 1. Reactants: magnesium metal, Mg (s), and 0.10 M HCI Observations Half-Reactions: Grayish Cloudy color bubbles, Phizzing Mt2 +2e-my 2H222 _H2 Or hed E° (V) Oxidation or Reduction? -2.360 OX Circle the reactant in each half-reaction. Calculation for Ecell-or explanation why calculation can't be done: -2.76U -> OU=+2.36V Ecoll +2.36v 2. Reactants: copper metal, Cu (s), and 0.10M AgNO. +234 ox Observations Small bubbles removes comer color to Silver color E° (V) "Oxidation or Reduction? Half-Reactions: Cuit+26 -> Cu cu +.80 Red Circle the reactant in each Kalf-reaction. Calculation for Ecellor explanation why calculation can't be done: .80 -.34 ..460 Agti té ->Ag Ecos 460 3. Reactants: copper metal, Cu (s), and 0.10 M HC Observations No heaction E° (V) Oxidation or Reduction? Half-Reactions: Circle the reactant in each half-reaction. Calculation for Ecell-or explanation why calculation can't be done: NO Edell reaction takes place because copper cant replace Hydrogen from Her, because of its low reactivity than hydrogen 5 Redox Reactions
esc sty JO MacBook 80 4. Reactants: 0.10 M Mg(NO), and 0.10 M Cu(NO) Observations_ light blue No bubbling E° (V) Oxidation or Reduction? Half-Reactions: Circle the reactant in each half-reaction. Calculation for Ecell - or explanation why calculation can't be done: Ecell Conclusions 1. What is the general pattern for the relative position of the two reactants for a spontaneous reaction to occur? 2. What are the two cases for a reaction to NOT occur? Describe each case in terms of the relative positions on the table of reduction potentials of the two reactants: Case A Case B PART (2) Note: show calculations as directed by the lab instructor 1. Reactants: copper metal, Cu(s), and 0.10 M Mg(NO3)2 Reaction: V Ecell AG kJ K Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: Took Shommes of copper away, looks dlacker 2. Reactants: zinc metal, Zn (s), and 3M HCl (or 6M) Reaction: use K Ecengles V kJ AG agus Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: Instantly bubbles, Smokey amc Heered black 6 Redox Reactions
MacBook Air will 80 23 2 3. 3. Reactants: 0.10 M Al(NO2)and 0.10 M AgNO, Reaction: Ecell AG kJ K Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: No reaction 4. Reactants: zinc metal, Zn(s) and 0.10 Cu(NO3)2 Reaction: Ecell V AG kJ Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: 2 mc turned black, light blue liquid 5. Reactants: copper metal, Cu (s), and 0.10 M Al(NO), Reaction: V Ecell AG kj K Prediction: Spontaneous / Not Spontaneous (or no reaction) Observations: Copper less Shisky, looks darker 6. Reactants: aluminum metal, Al(s), and 3 M HCl (or 6M) Reaction: s Ecoll 6.66 V AG -9,56210² k ko 10 Prediction: Spontaneous / Not Spontaneous (or no reaction) Spontaneous Observations: Bubbles gets bat, smokey creates condensation, final color is greyish/black. 7 | Redox Reactions