Question

5-7 help please !! due soon

S When 7.0 g of sodium hydroxide (NaOH) is dissolved in 238.5 g of water in an insulated container, the temperature rises from 20.00 oC to 27.66 oC. Calculate the molar enthalpy change (AH) for the dissolution process in kJ/mol NaOH A) -43.7 kJ/mol B) +45.0 kJ/ml C)-32.7 kJ/mol D) +32.7 kJ/mol E) -45.0 kJ/mol 6) Given the data in the table below, AH rxn for the reaction 4NH3 (g)+502 (8) -- 4NO (g) + 6H20 (1) kJ. Substance JAH°f (kJ/mo]) H20 () -286 NO (g) 90 NO2 (g) 34 HNO3 (aq) -207 NH3 (g) -46 O(g) 249 A) -1540 B)-150 C)-1892 D)-1172 E) The AH°fof O2 (g) is needed for the calculation. 7) Which of the following is a statement of Hess's law? A) The AH for a process in the forward direction is equal to the AH for the process in the reverse direction. B) The AH of a reaction depends on the physical states of the reactants and products C) If a reaction is carried out in a series of steps, the AH for the reaction will equal the sum of the enthalpy changes for the individual steps. D) If a reaction is carried out in a series of steps, the AH for the reaction will equal the product of the enthalpy changes for the individual steps. E) The AH for a process in the forward direction is equal in magnitude and opposite in sign to the AH for the process in the reverse direction.

Answer 1

Moles of NaOH = mass / molar mass = 7 / 40 = 0.175 moles

Energy released = mass of water * Specific heat * Temperature change = 238.5 * 4.184 * (27.66 - 20) = -7.643 KJ

Molar enthalpy = heat / number of moles = -7.643 / 0.175 = -43.67 KJ/mol

6) Enthalpy change = sum of enthalpy of formation of products - sum of enthalpy of formation of reactants

= (4 * 90 + 6 * -286) - (4 * -46 + 5 * enthalpy of formation of O₂)

We can't do it without thye missing value for oxygen

7) D.