Question

What are standard conditions of ΔH° for the data you will use?

Temperature

0 K

100 K

273 K

298 K

Pressure

1.0 Pa

100 Pa

1.0 bar

100 bar

Concentration

1.0 g/L

1.0 mol/L

1.0 mg/L

mol/kg

Select the complete reactions (including phases) for the reaction between solid NaOH and a solution of HCl.

2NaOH(s) + HCl(aq) → 2NaCl(aq) + H₂O(l)

NaOH(s) + HCl(aq) → NaCl(aq) + H₂O(l)

NaOH(s) + HCl(aq) → NaCl(s) + H₂O(l)

Calculate the theoretical ΔH°_r for the reaction you wrote in the question above. Use thermodynamic values from the table posted in LabArchives. Choose the correct answer below.

57.6 kJ/mol

100.3 kJ/mol

-57.6 kJ/mol

-100.3 kJ/mol

The questions below take you through the calculations you will need to complete with your experimental data. If you get a questions wrong, be sure to use the correct answer you are provided to continue to the next step in the calculations.

Following the procedure from the lab, a student added 61.0 mL of 1.0 M HCl to the calorimeter. After collecting temperature data for 100 s, she added 1.65 g of NaOH. She considered the start of the reaction 110 s, since that is when she finished adding the NaOH. She then collected temperature data for several more minutes.   The temperature data is given below. Questions 6-15 refer to this data.

time (s)	temp (oC)		time (s)	temp (oC)		time (s)	temp (oC)
0	20.5		190	32.9		330	36.6
20	20.5		200	33.8		340	36.5
40	20.5		210	34.6		350	36.5
60	20.5		220	35.3		360	36.5
80	20.5		230	35.8		370	36.4
100	20.5		240	36.1		380	36.4
110			250	36.3
120	21.6		260	36.5
130	23.5		270	36.6
140	25.5		280	36.6
150	27.4		290	36.6
160	29		300	36.6
170	30.7		310	36.6
180	31.8		320	36.6

How many moles of NaOH were used in this experiment?

0.10 mol NaOH

0.041 mol NaOH

0.020 mol NaOH

0.58 mol NaOH

How many moles of HCl were used in this experiment?

0.061 mol HCl

1.0 mol HCl

12.2 mol HCl

61 mol HCl

Is HCl or NaOH the limiting reagent?

HCl

            NaOH

            Neither is limiting

            Cannot determine from the information given.

Using the data given, select a temperature for t_i

20.5 °C

21.6 °C

20.5 K

36.4 K

Using the data given, select a temperature for t_f

20.5 °C

21.6 °C

36.4 °C

36.6 °C

Using the data given calculate Δt.

15.0 °C

15.9 °C

16.1 °C

18.3 °C

What is the mass of the reaction mixture?

1.65 g

60.0 g

62.2 g

63.9 g

What is the value of q_soln for this experiment?

4.30 kJ

16.6 kJ

42.0 kJ

246 kJ

What is the number of moles of the limiting reagent in this experiment?

0.0058 mol

0.041 mol

0.061 mol

42.0 mol

What is the ΔH°_r for this reaction based on the experimental data?

-105 kJ/mol

-0.18 kJ/mol

105 kJ/mol

0.18 kJ/mol

           

We know that if the sum of two reactions equals a third reaction, the sum of the ΔH° of the two reactions should equal the ΔH° of the third reaction. If you are having difficulty with this question, please see your instructor before lab. However, if you are still uncertain in lab, you may check with your instructor before proceeding.

Select the two separate reactions that sum to the reaction you wrote earlier (solid sodium hydroxide + aqueous hydrochloric acid), using only reagents available to you on the chemicals list for this lab (and deionized water)

NaOH(aq) → NaOH(s)

HCl(s) → HCl(aq)

NaOH(s) → NaOH(aq)

NaOH(aq) + HCl(aq) →H₂O(l) + NaCl(aq)

Describe how you will experimentally measure the ΔH°_rxn for the two reactions you described in part a. You don’t need to give a lot of detail, but give a general description and all volumes of liquids and/or masses of solids for any reagents used (including water). Do this for each reaction.

Answer 1