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13 Dec 2019

Chemical energy is released or absorbed from reactions in various forms. The most easily measurable form of energy comes in the form of heat, or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction:

?H?rxn=? np?H?f(products)?? nr?H?f(reactants)

where n represents the stoichiometric coefficients.

Calculate the standard enthalpy change for the reaction

2A+B?2C+2D

Use the following data:

Substance ?H?f
(kJ/mol)
A -247
B -413
C 213
D -475

?H?rxn =

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17 Dec 2019

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Related questions

Chemical energy is released or absorbed from reactions in various forms. The most easily measurable form of energy comes in the form of heat, or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction:

ΔH∘rxn=Σ npΔH∘f(products)−Σ nrΔH∘f(reactants)

where n represents the stoichiometric coefficients.

Calculate the standard enthalpy change for the reaction

2A+B⇌2C+2D

Use the following data:

Substance ΔH∘f
(kJ/mol)
A -231
B -407
C 219
D -497

1. Complete and balance the following chemical reaction: NH4NO3(s) + H2O(l) --> ?

Given

2. Volume of DI water used 50 mL

3. Mass of DI water 50 g

4. Initial temperature of water, Ti 22.5°C

5. Mass of NH4NO3 3.0 g

6. Moles of NH4NO3 ________0.0375__________mol

7. Final temperature of water, Tf 18.9°C

8. change in temperature of the water (?T) -3.6 °C

9. calculate the heat associate with water, qH2O ___ ___-752.4_____________ J

m*c* deltaT = (50g)(4.184 J/g*k)(-3.6) = -752.4

10. the heat either released or absorbed by the reaction (?Hrxn) ________+752.4____________ J

Question: [Please notice the units]

11. Calculate the change in enthalpy (?Hrxn) for this reaction. _____________ kJ ??

12. Calculate the heat of reaction in kJ per mole of NH4NO3 ______________ kJ/mol ??

13. If the heat capacity of the calorimeter was 25 J/oC, what would the new change in enthalpy (?Hrxn) for this reaction be? (Use equation 7 to recalculate the value from #10) ____________________ kJ/mol ?? [Equation 7: - q(rxn) = q(soln) + q(calorimeter)

14. Is this an exo- or endothermic reaction? Explain the reasoning behind your choice. ??

15. Calculate the change in enthalpy for the reaction (?Hrxn) per mole using equation 8 and Table 2. NH4NO3 (s) --> NH4NO3 (aq)

__________________kJ/mol ?? [Equation 8: ?Hrxn = sum{ n?Hf (products) - sum{ n?Hf (reactants)

16. What is the percent error between your value and the value calculated from 13? What are some possible sources of error in the experiment?

__________________% error

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