Mg + 2HCI --> MgCl2 + H2
0.158 g of Mg metal is combined with an excess of HCl to make 100.0 ml of solution in a coffee up calorimeter. The reaction rises from 25.60 C to 32.80 C. Determine delta H for the reaction of one mole of Mg. Units in kJ. 3 significant figures.
To determine the enthalpy change (ΔH) for the reaction of one mole of Mg, we can use the equation:
ΔH = q / n
where:
ΔH is the enthalpy change for one mole of the substance,
q is the heat absorbed or released by the reaction,
n is the number of moles of the substance involved in the reaction.
First, we need to calculate the heat (q) absorbed or released by the reaction using the equation:
q = mcΔT
where:
m is the mass of the solution in grams,
c is the specific heat capacity of the solution in J/(g·°C),
ΔT is the change in temperature of the solution in °C.
Given data:
Mass of Mg = 0.158 g
Volume of solution = 100.0 ml = 100.0 g (assuming the density of the solution is close to 1 g/ml)
Change in temperature (ΔT) = 32.80°C - 25.60°C = 7.2°C
Next, we need to find the number of moles of Mg reacted. Since the stoichiometry of the balanced chemical equation is 1:1 for Mg and HCl, the number of moles of Mg is the same as the number of moles of HCl.
To find the number of moles of HCl solution:
Volume of solution = 100.0 ml = 0.1 L
Concentration of HCl is not given, but since it is stated that there is an excess of HCl, we can assume it to be high enough to fully react with the Mg.
Now, we can calculate the number of moles of Mg using the molar mass of Mg:
Molar mass of Mg = 24.31 g/mol
Number of moles of Mg = mass of Mg / molar mass of Mg
Finally, we can substitute the values into the equation ΔH = q / n to calculate the enthalpy change (ΔH) for the reaction of one mole of Mg. Remember to convert the units to kJ.
Note: Make sure to use the appropriate specific heat capacity for the solution. If it is not given, you can assume it to be close to the specific heat capacity of water (approximately 4.18 J/g·°C).