the free energy for a reaction can be related to the equilibrium constant through the formula below. K = e (-ΔG° / RT) Therefore if Kc for a reaction is known, Go can be determined, or vice versa. Furthermore, if you have the value for Go at two different temperatures, you can calculate H and S through the familiar equation for Gibbs energy below, since you have two unknowns but also two equations. G = H – T S In this lab you will be studying the solubility of borax (Na2B4O5(OH)4*8H2O), a slightly soluble sodium salt, at two different temperatures. When solid borax is added to water, the equilibrium below is established. Na2B4O5(OH)4*8H2O (s) 2 Na+ (aq) + B4O5(OH)42- (aq) + 8 H2O(l) If you measure the concentrations for those substances that show up in the reaction quotient, then the Kc for the reaction at that temperature can be calculated. In this lab, the concentration of borate ion (B4O5(OH)42-) in solution will be measured by titration with standard hydrochloric acid according to the equation below. B4O5(OH)42- (aq) + 2 HCl (aq) + 3 H2O (l) 4 H3BO3 (aq) + 2 Cl- (aq) The concentrations of the other substances that appear in the reaction quotient can be calculated from the borate concentration using stoichiometry. Two Kc values with temperature Room temperature: 296 K and Kc: 0.00332 M Ice temperature: 277 K and Kc: 0.0000173 M When borax dissolves in water, are the products or the reactants favored? How does your value of Kc indicate this? Explain your answer.
the free energy for a reaction can be related to the equilibrium
constant through the formula below.
K = e (-ΔG° / RT)
Therefore if Kc for a reaction is known, Go can be determined, or vice versa. Furthermore, if
you have the value for Go at two different temperatures, you can calculate H and S through
the familiar equation for Gibbs energy below, since you have two unknowns but also two
equations.
G = H – T S
In this lab you will be studying the solubility of borax (Na2B4O5(OH)4*8H2O), a slightly soluble
sodium salt, at two different temperatures. When solid borax is added to water, the
equilibrium below is established.
Na2B4O5(OH)4*8H2O (s) 2 Na+ (aq) + B4O5(OH)42- (aq) + 8 H2O(l)
If you measure the concentrations for those substances that show up in the reaction quotient,
then the Kc for the reaction at that temperature can be calculated. In this lab, the
concentration of borate ion (B4O5(OH)42-) in solution will be measured by titration with standard
hydrochloric acid according to the equation below.
B4O5(OH)42- (aq) + 2 HCl (aq) + 3 H2O (l) 4 H3BO3 (aq) + 2 Cl- (aq)
The concentrations of the other substances that appear in the reaction quotient can be
calculated from the borate concentration using stoichiometry.
Two Kc values with temperature
Room temperature: 296 K and Kc: 0.00332 M
Ice temperature: 277 K and Kc: 0.0000173 M
When borax dissolves in water, are the products or the reactants favored? How does your value of Kc indicate this? Explain your answer.
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