Calculate the molar enthalpy for the following reaction.
HCl(aq) + NH3 (aq) --> NH4Cl (aq).
HCl = 50 ml (2.00M) NH3 = 50 ml (2.05 M)
Delta T = 9.28 degrees Celsius. Ccal = 28.9J/g degrees celcius.
The process is the same as the NaOH +HCl problem we did below. The only difference is Ccal is given and you calculate dH in kJ/mol.
I don't know the heat capacity of NH4Cl or the density of it, can you please help me figure those out.
I think you are supposed to assume the heat capacity of the NH4Cl solution is the same as that of water which is 4.184 J/g*C.
I think you are to assume that the density of the NH4Cl solution is the same as that of water or 1.00 g/mL which is the usual quoted value.
I was surprised that the NaOH/HCl problem used 3.91 for the solution instead of 4.184. Most of these problems assume the solutions to be the same as water and the density to be the same as water.
Thankyou Dr. Bob and can you please help me on one more question if this reaction goes to completion what would the final concentration of NH4Cl in the calorimeter. I know how to figure it out if its not in the calorimeter but I am wondering if the calculations are different when its inside a calorimeter.
I believe you are over thinking this. mols NH4Cl formed is the same whether we do it in a calorimeter or a bucket. mols mol HCl = M x L = 2.00M x 0.050L = 0100 mol. HCl is the limiting reagent (and it will go to completion) so this reaction produces 0.100 mol NH4Cl.
How much heat is released.
q, that letter again, = [mass H2O x specific heat H2O x delta T] + [Ccal x delta T] = 0
q = [100 x 4.184 x 9.28] + [28.9 x 9.28]= 0
Calculate q which of course is delta H for the reaction. This is the heat produced by the reaction.
You want delta H in kJ/mol.
Take your number which is in joules, convert to kJ, then dH/0.1 = dH in kJ/mol.
kik
To calculate the molar enthalpy (or heat) change of a reaction, you can use the equation:
q = m × C × ΔT
Where:
q is the heat change in Joules (J)
m is the mass in grams (g)
C is the specific heat capacity in J/g°C
ΔT is the change in temperature in degrees Celsius (°C)
Firstly, we need to find the mass of the solution. This can be calculated using the equation:
mass = volume × density
For the given reaction, we have both HCl and NH3 solutions, so we need to calculate their individual masses separately.
For HCl:
Volume of HCl solution = 50 mL = 50 cm³
Density of HCl solution is not provided, but assuming it is similar to water, we can use the density of water, which is approximately 1 g/cm³.
mass of HCl solution = volume × density = 50 cm³ × 1 g/cm³ = 50 g
Similarly, for NH3:
Volume of NH3 solution = 50 mL = 50 cm³
Density of NH3 solution is not provided, so we cannot calculate the mass based on the information given.
Next, we can calculate the heat change for HCl and NH3 separately using the equation mentioned earlier. However, we need to consider the dilution that occurs when mixing solutions.
Since the volume of both solutions is the same (50 mL), we can assume that the volumes of HCl and NH3 are equal in the final solution.
For HCl, the concentration is given as 2.00 M, so the moles of HCl can be calculated as follows:
moles of HCl = concentration × volume = 2.00 mol/L × 0.050 L = 0.10 mol
For NH3, the concentration is given as 2.05 M, so the moles of NH3 can be calculated as:
moles of NH3 = concentration × volume = 2.05 mol/L × 0.050 L = 0.1025 mol
Now that we have the moles of HCl and NH3, we can calculate the heat change using the equation:
q = m × C × ΔT
For HCl:
q(HCl) = (mass of HCl solution) × (Ccal) × (ΔT)
Ccal is given as 28.9 J/g°C, and ΔT is given as 9.28°C.
q(HCl) = 50 g × 28.9 J/g°C × 9.28°C = 13,376 J
For NH3:
q(NH3) = (moles of NH3) × (ΔH)
We need the enthalpy change of the reaction (ΔH) to calculate the heat change of NH3. The enthalpy change can be determined by finding the difference in bond energies between reactants and products. However, this information is not provided, so we cannot calculate the heat change for NH3.
In conclusion, based on the information given, we can calculate the heat change for HCl, which is equal to 13,376 J. However, we cannot calculate the heat change for NH3 without the enthalpy change (ΔH) of the reaction.