When 0.50 g of magnesium metal is placed in a calorimeter, and 100. mL of 1.0 M

Question

1. When 0.50 g of magnesium metal is placed in a calorimeter, and 100. mL of 1.0 M HCl were added the temperature of solution increased from 22.2 ºC to 44.2 ºC.  Assume that the specific heat of solution is 4.18 J/gºC and that the density is 1g/mL.Write a balanced equation for the above reaction.  Calculate the enthalpy of reaction per mole of magnesium. Use your value for Cp.  

1. When 0.50 g of magnesium metal is placed in a calorimeter, and 100. mL of 1.0 M HCl were added the temperature of solution increased from 22.2 ºC to 44.2 ºC.  Assume that the specific heat of solution is 4.18 J/gºC and that the density is 1g/mL.Write a balanced equation for the above reaction.  Calculate the enthalpy of reaction per mole of magnesium. Use your value for Cp.  

Explanation / Answer

Balanced reaction

Mg + 2HCl ----> MgCl2 + H2

Given,

Mass of Mg = 0.5 g

=> Moles of Mg = 0.5 / 24.3 = 0.0206 moles

Moles of HCl = 0.1 x 1 = 0.1 moles

Change in Temp (T2 - T1) = 44.2 - 22.2 = 22 degree C

Cp = 4.18 J/ g K

Total Volume of Solution = 100 mL

=> Mass of Solution = 100 x 1 = 100 g

Heat Gained by solution = m Cp (T2 - T1)

=> Heat Gained = 100 x 4.18 x 22 = 9196 J

For reaction of 0.0206 moles of Mg, Heat released = 9196 J

=> For reaction of 1 mole of Mg, heat released = 9196 / 0.0206 = 446407.8 J = 446.41 KJ

=> Enthalpy = - 446.41 KJ (-ve since energy is released)

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