Question

question 1 & 2

1. Magnesium solid reacts with aqueous hydrochloric acid to form the Mg2+ ion in solution. In an experiment, 60.0 mL of aqueous HCI was mixed with 0.1297 g of magnesium solid in a double Styrofoam cup calorimeter. The reaction caused the temperature of the substances in the calorimeter to rise 10.02°C. Assume the density and specific heat of the HCl solution is that of water, 1.00 g/mL and 4.184 J/g °C, respectively. The specific heat of magnesium is 1.02 J/g °C. a. Write the balanced chemical equation for this reaction. b. Calculate the heat of this reaction, AHpx, in kJ. c. Calculate the heat of this reaction per mole of Mg2+ formed, AHx/mole Mg d. The literature value of this reaction is 466.85 kJ/mole. Calculate the percent deviation of the experimental value from the literature value. 2. A 45.5 kg copper rod (s = 0.385 J/g °C) is heated to 475.0°C and then quenched into a well-insulated water bath containing 1000.0 kg of water at 25.0°C. What is the final temperature of the mixture?

Answer 1

1) a)

Mg(s) + 2HCl(aq) = M9 + 2C1jag) + H2,(0)

b) The heat can be calcualted using:

q= -m.C.47

Where m is the mass of the system C is its heat capacity and delta T is the change in temperature. Sin the density is 1 g/mL, the mass of HCl is the same as the volume, numerically, and we have:

9 = -60.1297g .4.184– . 10.02°C = -2521J = -2.521kJ 10.09 9.

(The negative sign is beacuse this is heat given by the reaction to the surroundings).

c) The number of moles of Mg that were added is:

n = m mmolar 0.12979 = 0.005336 moles 24.305g/mol

So the heat released per mole is:

-2.521kJ 0.005336 moles = -472.4 mol

d) The percent difference with the given value is:

(-472.4-(-466.85)) V = 1.193 -466.85

1.193%.

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The heat lost by the copper rod is the same as the heat gained by the water:

mrod · Crod · (Tf,rod - Torod) = -mw.cw . (Tfw – Tow)

The final temperature of both is the same, since they are together, we will name this Tf. Rearranging:

r. T = To,rod · Crod Mrod + To,w.Cwmv Crod. mrod + Cw.mw 475.0°C -0.3856620.45.5kg + 25.0°C • 4.184 kr. 1000.0kg 0.385m. 45.5kg + 4.184km 6. 1000.0kg 26,88°C