1. The standard enthalpy of formation for solid calcium phosphate is-4132 kJ/mol
ID: 571643 • Letter: 1
Question
1. The standard enthalpy of formation for solid calcium phosphate is-4132 kJ/mol. a. Write the net ionic equation for the precipitation of calcium phosphate that results from mixing an aqueous solution containing calcium nitrate with an aqueous solution containing sodium phosphate. (4 pts) b. Calculate the standard enthalpy for this reaction. (4 pts) 2. The reaction described in problem #1 is the focus of a calorimetry experiment which generates the following data: A dry coffee-cup calorimeter is weighed on a balance; its mass is 6.001 g 25.0 mL of 2.27 M sodium phosphate solution is added to the calorimeter; the mass of the calorimeter with this solution volume is measured to be 30.722 g. - 25.0 mL of 3.15 M calcium nitrate solution is mixed with the sodium phosphate solution already in the calorimeter; after a maximum temperature change is achieved, the mass of the calorimeter and its contents is measured to be 55.489 g. Based on this data and the standard enthalpy of the reaction calculated in problem #1, determine the following (for the values of density and specific heat, assume the aqueous solutions are pure water): a. Calculate the amount of heat generated or absorbed by the reaction based on the moles of phosphate added to the calorimeter. (5 pts) b. Calculate the amount of heat generated or absorbed by the reaction based on the moles of calcium added to the calorimeter. (5 pts) c. Given that the calorimeter is composed of styrofoam (specific heat is 1.13 Jg C) and the initial temperature of the reaction mixture is 22.7, calculate the final temperature of the reaction mixture after the maximum temperature change is achieved. (7 pts)Explanation / Answer
1) Balanced reaction:
3Ca(NO3)2 (aq)+ 2Na3PO4(aq) ----->Ca3(PO4)2(s)+6NaNO3(aq)
ionic equation:
3Ca2+(aq) +2NO3- (aq) +6 Na+(aq) +2PO4- (aq)---->Ca3(PO4)2(s)+6Na+(aq)+6NO3-(aq)
removing all spectator ions:
3Ca2+(aq) +2PO4- (aq)---->Ca3(PO4)2(s) [net ionic equation]
This equation shows the formation of 1 mol calcium phosphate, so enthalpy for the reaction=enthalpy of formation of calcium phosphate =-4132KJ
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