Question

Use the following data to work through problems 4-6.

• 50.0 mL of each solution was used in each experiment.
• Each solution had a molarity of 2.00 M.
• The density of the solutions once mixed are 1.03 g/mL.
• The following table is data collected from an actual experiment.

	Initial Temp	Final Temp	Temp Change
NaOH + HCL	19.85	33.07	13.2
NaOH+ NH4Cl	19.78	20.40	0.62
HCl + NH3	20.16	32.05	11.89

1. Calculate the amount of heat energy, q_surroundings, produced in each reaction. Use 03 g/mL for the density of all solutions. Use the specific heat of water, 4.184 J/(g•°C), for each of the three reactions. q_surroundings = C_s ´ m ´ ∆T

2. Calculate the enthalpy change, ∆H_reaction, per mole of reactant for each of the three reactions in units of kJ/mole.

                                    ∆H_reaction = ∆H_system

3. Calculate a percent error between the accepted values for ∆H_reaction(use values calculated in question 1 as accepted values) and the “experimental” values you calculated in question 5 for each reaction.

                                               

                        % Error = Experimental – Accepted x 100

                                                Accepted

Answer 1

In this case, the volume, concentration and density conditions for each of the solutions will be considered the same. Therefore, the values of mass and moles are determined for each reaction:

To calculate the enthalpy of reaction:

For the calculation for each mole, then:

And so for each reaction, getting:

To calculate the percentage deviation, it is necessary to calculate the standard formation enthalpy with theoretical values, using the equation:

According to the exercise, the values have already been calculated previously. In any case, here are the theoretical formation values (Kj/mol) for each compound:

NaOH	469,4
HCl	92,31
NaCl	411
H2O	285,84
NH3	67,20
NH4Cl	315,4

For the reaction 1, so:

%

And so on:

As can be seen, the deviation percentages are very high. Remembering that it is perhaps necessary to perform a correction factor according to the ambient temperature, since the reaction enthalpies used are at a temperature of 25C. Or, verify the user values with the dice with the teacher and perform the same calculations again.