Aqueous silver ion reacts with aqueous chloride ion to yield a white precipitate of solid silver chloride. When 10.0 mL of 1.00M AgNO3 solution is added to 10.0mL of 1.00 M NaCl solution at 25oC in a calorimeter a white precipitate of AgCl forms and the temperature of the aqueous mixture increases to 32.6oC. Assuming that the specific heat of the aqueous mixture is 4.18 J/goC, that the density of the mixture is 1.00 g/mL, and that the calorimeter itself absorbs a negligible amount of heat, calculate the amount of heat absorbed in kJ/mol of Ag+.

Explanation:

AgNO3 + NaCl --> AgCl + NaNO3

Number of moles

AgNO3

= molar concentration * volume

= 1 * 0.01

= 0.01 mol

NaCl

= 0.01 * 1

= 0.01 mol.

By stoichiometry, 1 mole of silver nitrate reacted with 1 mole of NaCl. Therefore,

Number of moles of AgCl formed = 0.01 × 1

= 0.01 mol AgCl formed.

Heat absorbed by solution during precipitation:

Mass of solution = density × total volume

= 1 × 20

= 20 g.

q = m * Cp * (T2 - T1)

= 20 * 4.18 * (32.6 - 25.0)

= 635 J

Since 635 J was absorbed by the solution, the reaction released -635 J

So, Delta H = -635 J/0.01 mol

= -63500 J/mol

= -63.5 kJ/mol.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.