NH4NO3(s) NH4+(aq) + NO3−(aq)
In order to measure the enthalpy change for this reaction above, 1.07 g of NH4NO3 is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8°C and the final temperature (after the solid dissolves) is 22.4°C. Calculate the change in enthalpy for the reaction in kJ. (Use 1.0 g/mL as the density of the solution and 4.18 J/g · °C as the specific heat capacity.)
We've been doing a lot of energy problems, but I'm not sure how to begin this one. I don't want the answer, just the set up so I know what I'm doing. Thanks. :)
The rise is T for H2O is your route to heat involved.
q = mass H2O x specific heat H2O x delta T.
Then q/1.07 = delta H/gram.
Usually these are quoted in kJ/mol.
(delta H/gram NH4NO3) x molar mass NH4NO3 x (1 kJ/1000 J) = ?
Note: Since T went down you know it was cooled and means an endothermic reaction so the sign of delta H is +.
I think you can report more than 2 significant figures.
I calculated 26.6 kJ/mol.
To calculate the change in enthalpy for the given reaction, we can use the formula:
ΔH = q / n
Where:
ΔH is the change in enthalpy (in kJ)
q is the heat absorbed or released by the reaction (in J)
n is the number of moles of NH4NO3 involved in the reaction.
To calculate q, we need to determine the heat absorbed or released by the 25.0 mL solution of NH4NO3. We can do this using the formula:
q = mcΔT
Where:
q is the heat absorbed or released (in J)
m is the mass of the solution (in g)
c is the specific heat capacity of the solution (in J/g · °C)
ΔT is the change in temperature (final temperature - initial temperature, in °C)
First, we need to determine the mass of the solution. Since the density of the solution is given as 1.0 g/mL and the volume of the solution is 25.0 mL, the mass of the solution can be calculated as:
mass of the solution = density × volume of the solution
mass of the solution = 1.0 g/mL × 25.0 mL
mass of the solution = 25.0 g
Next, we can calculate q using the formula mentioned earlier:
q = mcΔT
q = (25.0 g) × (4.18 J/g · °C) × (22.4°C - 25.8°C)
Now, to determine the number of moles of NH4NO3 involved in the reaction, we need to use the molar mass of NH4NO3, which is 80.0434 g/mol.
moles of NH4NO3 = mass of NH4NO3 / molar mass of NH4NO3
moles of NH4NO3 = 1.07 g / 80.0434 g/mol
Finally, we can substitute the values of q and n into the formula for ΔH to calculate the change in enthalpy for the reaction:
ΔH = q / n
This will give you the change in enthalpy for the reaction in kJ. Make sure to perform the calculations and unit conversions carefully to obtain the accurate value.