Question

What would be the effect of each of the following sources of error in the reaction between Mg and HCl? Would they result in a high, low, or unaffected value for the heat of reaction? Why?

A. The calorimeter absorbs heat.
B. The thermometer reads 2 °C low at all temperatures.
C. The actual molarity of the HCl is slightly higher than reported on the bottle.

D. The mass of the filter paper was not subtracted in the determination of ∆H1.

Answer 1

Magnesium metal or Mg ribbon will vigorously react with HCl to from MgCl2 and releasing ample amount of heat in the reaction

a) The calorimeter absorbs heat

If the calorimeter will absorb the heat, the delta H of the reaction which was more negative will become less negative, hence delta H will reduce in magnitude but will increase due to negative sign

b) The thermometer reads 2C low at all temperatures

The Delta H will be lesser negative value at lower temperature since with the decrease in temperature the reaciton will not be spontatneous

Hene the correct answer is it will increase due to the presence of negative sign

c)

It will decrease since more the number of moles of HCl, more products will be formed, hence the value of Delta H will become more and moer negative

Therefore the value of Delta H will decrease in value but the magnitude will be increased

d)

It will not affect the Delta H value and it will remain constant