1. Using values from Appendix 3 of Chang’s Chemistry, calculate the standard ent
ID: 921210 • Letter: 1
Question
1. Using values from Appendix 3 of Chang’s Chemistry, calculate the standard enthalpy change for the following reaction: AgNO3 (aq) + Br2 (g) AgBr (s) + Na+ (aq)
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2-Write an overall equation for the formation of gaseous diborane (B2H6) and determine the standard enthalpy of formation of B2H6 using the following information:
4B (s)+3O2 (g)2B2O3 (s)H = -2509.1 kJ
2H2 (g)+O2 (g) 2H2O (l)H = -571.7 kJ
B2H6 (g) +3O2 (g)B2O3 (s)+3H2O (l)H = -2147.5 kJ
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3.Liquid benzene C6H6 (l) will decompose to gaseous acetylene C2H2 (g) in the following reaction:
1/3C6H6 (l) C2H2 (g)H = +210.0 kJ
What is the enthalpy change for the reverse reaction?
What is the enthalpy change for the decomposition of 1 mole of benzene to acetylene?
Would the forward reaction or the reverse reaction be more likely to be thermodynamically favored?
If C6H6 (g) were consumed instead of C6H6 (l), would you expect the magnitude of the enthalpy change to increase, decrease or remain constant?
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Consider a hydrogen atom. For each of the following electron transitions, calculate the energy, frequency and wavelength of the associated radiation and determine if the radiation is being released or absorbed.
From n = 5 to n = 1
From n = 4 to n = 5
From n = 6 to n = 2
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Which of the following are allowable quantum numbers for an electron in a hydrogen atom? Select all that apply.
N = 2, l = 1, ml = 1
N = 1, l = 0, ml = -1
N = 4, l = 2, ml = -2
N = 3, l = 3, ml = 0
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Consider the following valence-level orbital diagram.
Identify the element from this valence-level diagram.
Draw a Lewis dot symbol for this element.
List all other symbols of the elements in its group and rank them all in terms of increasing atomic radius.
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1.Using electron configurations, explain why the electron affinity for Fluorine is a negative value, whereas the electron affinity for Neon is a positive value.
2.Arrange the following elements in terms of increasing atomic radius: F, P, S, As
3.Arrange the following in terms of increasing ionic radius: C-1, C+2, C0, C+1, C -3
4.Rank the following elements in terms of increasing reactivity: Ca, Mg, K
Explanation / Answer
1. [you have not given the values of H°f of the reactants and products.. You have to use the following equation...]
AgNO3 (aq) + Br2 (g) --> AgBr (s) + Na+ (aq)
standard enthalpy change for the reaction,
dHo = H°fproducts - H°freactants
2. overall equation for the formation of gaseous diborane: 2B(s) + 3H2 (g)= B2H6 (g)
4B (s)+3O2 = (g)2B2O3 (s) H = -2509.1 kJ .......[1]
2H2 (g)+O2 = (g) 2H2O (l) H = -571.7 kJ.....[2]
B2H6 (g) +3O2 = (g)B2O3 (s)+3H2O (l) H = -2147.5 kJ.........[3]
adding 0.5*[equation 1] + 1.5[equation 2] we get,
2B (s) + 3O2 + 3H2 (g ) = (g)B2O3 (s)+3H2O (l) H = 0.5(-2509.1 kJ) + 1.5(-571.7 kJ) = -2112.1 kJ.....[4]
Subtracting equation [3] from [4] we get,
2B(s) + 3H2 (g)= B2H6 (g) H = -2112.1 kJ - (-2147.5 kJ) = 35.4 kJ
standard enthalpy of formation of B2H6 = 35.4 kJ
3. The enthalpy change for a reaction is equal in magnitude, but opposite in sign, to H for the reverse reaction.
So enthalpy change for the reverse reaction is -210.0 kJ.
Enthalpy change for the decomposition of 1 mole of benzene to acetylene = 3*210 = 630kJ
The reverse reaction would be more likely to be thermodynamically favored because of the negative value of dH.
If C6H6 (g) were consumed instead of C6H6 (l), the magnitude of the enthalpy change would decrease because here less energy would be required to form the gaseous molecules of acetylene. Previously more energy need to be supplied to convert the liquid molecules into gaseous molecules.
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