 # Chemistry Questions

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For the gas phase reaction reaction 2 502 + 02 : 2 503 (g) [5021eq = 0.51 M eq = 0.35 M eq = 1.43 M at 827°C. What is the value of KC at this temperature? KC is calculated using the equation: KC = [products]F’/[reactants]r where p and r are the stoichiometric coefficients for the products and reactants in the balanced equation and the concentrations are in M (moi/L). Incorrect. Tries 3/10 Previous Tries It is often necessary to use the thermodynamic equilibrium constant, K. K is related to KC by the equation: K = KC (RT)An (also seen as Kp = KC (RT)An in your text) where An = moles of gas in the products - moles of gas in the reactants R = the gas constant = 0.08206 T = temperature (K) Calculate K for this reaction at this temperature. Find the heat of the reaction using bond energies for the reaction shown above: Bond Bond Energies kJ/mol C-H 413 C-C 347 C=C 614 C-0 358 C=O 799 O-H 467 N-H 391 H-CI 427 C-CI 339 C-N 305 C EC 839 State your answer in k]. For a chemical reaction, the approximate AH can be calculated with the formula: q = Zbonds broken - Zbonds formed Sum the bond energies of the bonds broken in the reactants and subtract from that the sum of the bond energies of the bonds formed in the products. Bond breakage is endothermic and bond formation is exothermic. Use the following equations to calculate the heat of the reaction for the reduction of iron oxide to iron with carbon monoxide. 3Fe203(s) + C°(9) —> 2F6304(5) + C02(9) A H" = -58 kJ Fe304(5) + C0(9) —> 3Fe0(S) + C02(9) A H0 = 38 kJ Fe0(S) + C0(9) —> Fe(S) + C02(9) A H" = -17 kJ Calculate AHO for the following reaction: Fe203(s) + 3C0(g) —> 2Fe(s) + 3C02(g) Use k] for your answer. Use the reactions in the chart to create the reaction of interest. The reactions can be reversed to turn reactants into products or vice versa. If you do this, remember to also change the sign of AH”. The reactions can also be multiplied by new factors to give the correct overall reaction. Remember to multiply AH” by the same factor. Incorrect. Tries 1/10 Previous Tries Find the heat of formation for a mole of nitrogen dioxide (N02) given: 2N205(S) —> 4N02(9) + 02(9) A H" = 219 kJ N2(9) + 5/202(9) —> N205(S) A H0 = -43.1 kJ Use k] and 3 significant figures for your answer. AH°f of nitrogen dioxide (N02) = In a formation reaction you form one mole of the product and the reactants must all be elements in their most common states. Write out the formation reaction and then use Hess‘ Law, and the reactions that you are given, to calculate its AH. Incorrect. Tries 1/10 Previous Tries Heating Curve of Water Eva p0 ratio n 1 DD Condensation 50 Water Melting B —" c ‘—. FreeZI ng I“ Ice Joules The graph above shows the heating curve of water. Use this graph to answer the following question. What is the value of q when 44 g of water at 53.0°C is changed to 44 g of ice at —7.0°C (Celsius)? spec. heat of H20 = 4.184 J/g°C spec. heat of ice = 2.087 J/g°C Heat of Fusion = 6.02 kJ/mol 1 mol of water = 18.09 Include the units (kJ) in your answer. q = I: This will be a multi-step process. First, the temperature of the water must be lowered to its freezing temperature, 0°C. Use the formula: q1 = Cwater * AT * amount Remember that AT is Tﬁnal - Tinitial and C is the heat capacity of water. Now you have water at 0°C. Next you need to freeze the water. This occurs at a constant temperature, 0°C. Here, use the equation: ‘12 = ' AHfusion * amount Now you have ice at 0°C. Finally, the temperature of the ice changes. Use the formula: q3 = Cice * AT * amount Then add the three heat values to get the total heat given off. Pay special attention to units! All q values must have the same units, J or k], and the heat capacities and heats of fusion and vaporization will be expressed as either J/g or J/mol. Use the proper amount (g or moi) when doing the calculations. Heating Curve of Water Eva p0 ratio n 1 DD Condensation 50 Water Melting B —" c ‘—. FreeZI ng I“ Ice Joules The graph above shows the heating curve of water. Use this graph to answer the following question. How much heat is required to change 56 g of ice at -9.00°C (Celsius) to 56 g of steam at 113.0°C? For your answer, enter the value of q. spec. heat of H20 = 4.184 J/g°C spec. heat of ice = 2.087 J/g°C spec. heat of steam = 1.996 J/g°C Heat of Fusion = 6.02 kJ/mol Heat of Vaporization = 40.7 kJ/mol 1 mol of water = 18.09 Include the units (kJ) in your answer. —n-m- a-‘w .1111qu ﬂ— I . 11¢ . “Ii ' _ WM:- imam-H1“ Use the following equations to calculate the heat of the reaction for the formation of ethanol. C2H50H(I) + 302 —> 2C02(g) + 3H20(|) A H° -1367 kJ C(gr) + 02(9) —> C02(9) A H° = -394 kJ H2(9) + 1/2 02(9) —> H20(|) A H° = -286 kJ Calculate AHO for the following reaction: 2C(gr) + 3H2(g) + 1/2 02(9) —> C2H50H(l) ethanol Use k] for your answer. For the reaction: CaCZ (s) + 2 H20 (I) : Ca(OH)2 (s)+ CZHZ (9) write the equilibrium expression. For species that belong in the numerator (top) enter the coefficient (1,2,3, etc) For species that belong in the denominator (bottom) enter the coefficient as - coefficient (A'1 is 1/[A], A'2 is 1/[A]2, etc) If a species should not appear in the equilibrium expression, its coefficient should be 0. Anything raised to the zero power = 1, which is the activity of solids or pure liquids. Kc = [Ca(OH)2] |1 |[c2H2] |2 |[CaC2] |1 |[H20] |1 | Solids and pure liquids do not appear in equilibrium expressions. If they are present, their activity is 1. If they are absent, their activity is 0. The concentrations of reactants appear in the denominator and will have negative exponents. Incorrect. Tries 1/10 Previous Tries For the gas phase reaction reaction 2 502 + 02 : 2 503 (g) [5021eq = 0.51 M eq = 0.35 M eq = 1.43 M at 827°C. What is the value of KC at this temperature? KC is calculated using the equation: KC = [products]F’/[reactants]r where p and r are the stoichiometric coefficients for the products and reactants in the balanced equation and the concentrations are in M (moi/L). Incorrect. Tries 3/10 Previous Tries It is often necessary to use the thermodynamic equilibrium constant, K. K is related to KC by the equation: K = KC (RT)An (also seen as Kp = KC (RT)An in your text) where An = moles of gas in the products - moles of gas in the reactants R = the gas constant = 0.08206 T = temperature (K) Calculate K for this reaction at this temperature.

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