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11 Nov 2019

Use Hess’s Law to determine ΔH for the first 2 reactions and then add them together to determine ΔH for the third reaction: NH3 + HCl --> NH4Cl.

First two reactions:

NaOH+ HCl --> H2O + NaCl

NaOH + NH4Cl --> NH3 + NaCl + H2O

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Nelly StrackeLv2
2 Jan 2019

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Related questions

What is the relationship between the class average values of ΔH for reactions #1-3 that is consistent (within experimental error) with the relationship between the reactions themselves that you noted in question 3 above? Explain this relationship being sure to address the experimental error.

In "question 3" I noted that If we add reactions #1 and #3, we get reaction #2. This is an example of Hess’ Law. This states that regardless of the steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. These are the reactions

Rxn #1: NaOH(s) --->NaOH(aq)

Rxn #2: NaOH (s) + HCl (aq) ---> H2O (l) + NaCl (aq)

Rxn #3: NaOH (aq) + HCl (aq) -- > H2O (l) + NaCl (aq)

This is the class average:

Average -38.7 -87.5 -52.8
Maximum -47.4 -102.0 -71.5
Minimum -31.9 -61.0 -27.9
Absolute Error 8 21

22

Reaction NaOH and HCl

Trial Initial NaOH final NaOH+HCl
1 21.12°C 34.83°C
2 21.38°C 34.74°C
3 21.35°C 34.81°C
4 21.59°C 35.00°C

Reaction NaOH and NH4Cl

Trial Initial NaOH final NaOH+NH4Cl
1 21.10°C 22.24°C
2 21.19°C 22.48°C
3 21.10°C 22.52°C
4 21.21°C 22.62°C

Reaction HCl and NH3

Trial Initial HCl Final HCl and NH3
1 21.47°C 34.04°C
2 21.31°C 33.92°C
3 20.96°C 33.78°C
4 21.17°C 33.66°C

Calculate the expected (theoretical)molar enthalpies for the reactions.

With these values demonstrate Hess’s Law by calculating the enthalpy ofreaction 3 and comparing it to value obtained from (reaction 1 – reaction 2).

Calculate the molar enthalpy associated with each of the trials

* Determine the heat of reaction, q, for each trial

* Convert volume quantities to mole quantities

* Determine the molar enthalpy for each trial in kJ/mol

Use the experimental values to verify that Hess’s Law

* If data is not consistent with Hess’s Law comment on anyexperimental parameter that may have skewed the result.

******Please provide a concise explanation, thank you.*********

  1. You will investigate three reactions in this experiment. In thespace provided below, write the balanced molecular and net ionicequations from the descriptions of the reactions. Use the table ofstandard heats of formation in your text (or another approvedresource) to calculate the molar enthalpies of the reactions.
  • Reaction 1: An aqueous solution of sodium hydroxide reacts withan aqueous solution of hydrochloric acid, yielding water.

  • Reaction 2: An aqueous solution of sodium hydroxide reacts withan aqueous solution of ammonium chloride, yielding aqueous ammonia,NH3, and water.

  • Reaction 3: An aqueous solution of hydrochloric acid reacts withaqueous ammonia, NH3, yielding aqueous ammonium chloride.

Reaction

Balanced Reaction Equation

?H (KJ)

1

NaOH(aq) + HCl(aq) -> NaCl(aq) + H2O(l)

Net ionic: H+ (aq) + OH- (aq) -> H2O (l)

2

NaOH(aq) + NH4Cl(aq) -> NaCl(aq) + NH3(g) + H2O(l)

Net ionic: NH4+ (aq) + OH- (aq) -> NH3(g) + H2O(l)

3

HCl(aq) + NH3(aq) -> NH4+ + Cl-

Net ionic: H+ (aq) + NH3 (aq) -> NH4+
  1. For each reaction you perform, you will mix together 50.0 mL of2.00 M acid and 2.00 M base. What are the resulting concentrationsof the reactants upon mixing?
  2. How many moles of each reactant are present in each trial?
  3. What is the total volume of the solutions upon mixing? Assuminga density of 1.03 g/mL for the solution, find the total mass ofeach reaction mixture.

Hello, I have what I think are the right balanced equations butI can't figure out how to calculate the enthalpy (delta H) and I'munsure of how to do questions 1, 2, and 3 after the table.

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