Question 6Determine Whether The Reactions Are Spontaneous Or Non-spontaneous At 298.15 K 298.15 \, \text{K} 298.15 K .a) $4 , \text{NH}_3(g) + \text{O}_2(g) \rightarrow 2 , \text{N}_2\text{H}_4(g) + 2 ,

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Introduction

In the realm of chemistry, spontaneity is a crucial concept that determines whether a chemical reaction will occur on its own or not. The spontaneity of a reaction is influenced by various factors, including the change in Gibbs free energy (ΔG), temperature, and the concentrations of reactants and products. In this article, we will delve into the world of spontaneity and explore how to determine whether a reaction is spontaneous or non-spontaneous at a given temperature.

What is Spontaneity?

Spontaneity refers to the tendency of a chemical reaction to occur on its own without any external influence. A spontaneous reaction is one that is thermodynamically favored, meaning that it will proceed in the forward direction with a positive change in entropy and a negative change in Gibbs free energy (ΔG < 0). On the other hand, a non-spontaneous reaction is one that is thermodynamically unfavorable, meaning that it will not proceed in the forward direction without an external input of energy (ΔG > 0).

Gibbs Free Energy: The Key to Spontaneity

Gibbs free energy (ΔG) is a thermodynamic property that determines the spontaneity of a reaction. It is defined as the energy available to do work in a system at constant temperature and pressure. The change in Gibbs free energy (ΔG) is calculated using the following equation:

ΔG = ΔH - TΔS

where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

Determining Spontaneity: A Step-by-Step Approach

To determine whether a reaction is spontaneous or non-spontaneous, we need to calculate the change in Gibbs free energy (ΔG) using the equation above. Here's a step-by-step approach to determine spontaneity:

  1. Calculate the change in enthalpy (ΔH): This can be done using the standard enthalpy of formation (ΔHf) values of the reactants and products.
  2. Calculate the change in entropy (ΔS): This can be done using the standard entropy (S) values of the reactants and products.
  3. Calculate the change in Gibbs free energy (ΔG): Using the equation ΔG = ΔH - TΔS, we can calculate the change in Gibbs free energy at a given temperature.
  4. Determine spontaneity: If ΔG < 0, the reaction is spontaneous. If ΔG > 0, the reaction is non-spontaneous.

Example 1: Spontaneity of the Reaction between Ammonia and Oxygen

Let's consider the reaction between ammonia (NH3) and oxygen (O2) to form hydrazine (N2H4):

4 NH3(g) + O2(g) → 2 N2H4(g) + 2 H2O(g)

To determine the spontaneity of this reaction, we need to calculate the change in Gibbs free energy (ΔG) at 298.15 K.

Step 1: Calculate the change in enthalpy (ΔH)

Using the standard enthalpy of formation (ΔHf) values, we can calculate the change in enthalpy as follows:

ΔH = ΣΔHf(products) - ΣΔHf(reactants) = (2 × ΔHf(N2H4) + 2 × ΔHf(H2O)) - (4 × ΔHf(NH3) + ΔHf(O2)) = (2 × -132.2 kJ/mol + 2 × -241.8 kJ/mol) - (4 × -45.9 kJ/mol + 0 kJ/mol) = -106.4 kJ/mol

Step 2: Calculate the change in entropy (ΔS)

Using the standard entropy (S) values, we can calculate the change in entropy as follows:

ΔS = ΣS(products) - ΣS(reactants) = (2 × S(N2H4) + 2 × S(H2O)) - (4 × S(NH3) + S(O2)) = (2 × 217.8 J/mol·K + 2 × 188.8 J/mol·K) - (4 × 192.5 J/mol·K + 205.1 J/mol·K) = 12.3 J/mol·K

Step 3: Calculate the change in Gibbs free energy (ΔG)

Using the equation ΔG = ΔH - TΔS, we can calculate the change in Gibbs free energy at 298.15 K:

ΔG = ΔH - TΔS = -106.4 kJ/mol - (298.15 K × 12.3 J/mol·K) = -106.4 kJ/mol - 3.67 kJ/mol = -110.1 kJ/mol

Step 4: Determine spontaneity

Since ΔG < 0, the reaction is spontaneous.

Conclusion

In conclusion, spontaneity is a crucial concept in chemistry that determines whether a chemical reaction will occur on its own or not. By calculating the change in Gibbs free energy (ΔG) using the equation ΔG = ΔH - TΔS, we can determine whether a reaction is spontaneous or non-spontaneous. In this article, we have explored the concept of spontaneity and provided a step-by-step approach to determine spontaneity using the reaction between ammonia and oxygen as an example.

References

  • Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
  • Chang, R. (2010). Chemistry (10th ed.). McGraw-Hill.
  • Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.

Further Reading

For further reading on spontaneity and thermodynamics, we recommend the following resources:

  • Atkins, P. W. (2007). Four laws that limit life: and how they apply to you. Oxford University Press.
  • Leach, A. G. (2005). Molecular modelling: principles and applications (2nd ed.). Prentice Hall.
  • Scott, R. A. (2010). Chemical thermodynamics: an introduction. Wiley-Blackwell.

Glossary

  • Spontaneity: The tendency of a chemical reaction to occur on its own without any external influence.
  • Gibbs free energy (ΔG): A thermodynamic property that determines the spontaneity of a reaction.
  • Enthalpy (ΔH): A thermodynamic property that determines the energy change of a reaction.
  • Entropy (ΔS): A thermodynamic property that determines the disorder or randomness of a system.
    Spontaneity of Chemical Reactions: A Q&A Guide =====================================================

Introduction

In our previous article, we explored the concept of spontaneity in chemical reactions and provided a step-by-step approach to determine spontaneity using the reaction between ammonia and oxygen as an example. In this article, we will answer some frequently asked questions (FAQs) related to spontaneity and thermodynamics.

Q&A

Q: What is the difference between spontaneity and non-spontaneity?

A: Spontaneity refers to the tendency of a chemical reaction to occur on its own without any external influence. Non-spontaneity, on the other hand, refers to the tendency of a chemical reaction to not occur on its own without any external influence.

Q: How do you determine the spontaneity of a reaction?

A: To determine the spontaneity of a reaction, you need to calculate the change in Gibbs free energy (ΔG) using the equation ΔG = ΔH - TΔS. If ΔG < 0, the reaction is spontaneous. If ΔG > 0, the reaction is non-spontaneous.

Q: What is the significance of Gibbs free energy (ΔG) in determining spontaneity?

A: Gibbs free energy (ΔG) is a thermodynamic property that determines the spontaneity of a reaction. A negative ΔG value indicates that the reaction is spontaneous, while a positive ΔG value indicates that the reaction is non-spontaneous.

Q: Can a non-spontaneous reaction become spontaneous under certain conditions?

A: Yes, a non-spontaneous reaction can become spontaneous under certain conditions, such as an increase in temperature or a change in the concentrations of reactants and products.

Q: What is the relationship between entropy and spontaneity?

A: Entropy (ΔS) is a thermodynamic property that determines the disorder or randomness of a system. A positive ΔS value indicates an increase in entropy, which can contribute to the spontaneity of a reaction.

Q: Can a reaction be spontaneous at one temperature but non-spontaneous at another temperature?

A: Yes, a reaction can be spontaneous at one temperature but non-spontaneous at another temperature. This is because the change in Gibbs free energy (ΔG) is temperature-dependent.

Q: How do you calculate the change in enthalpy (ΔH) and entropy (ΔS) for a reaction?

A: To calculate the change in enthalpy (ΔH) and entropy (ΔS) for a reaction, you need to use the standard enthalpy of formation (ΔHf) and standard entropy (S) values of the reactants and products.

Q: What is the significance of the equation ΔG = ΔH - TΔS in determining spontaneity?

A: The equation ΔG = ΔH - TΔS is a fundamental equation in thermodynamics that relates the change in Gibbs free energy (ΔG) to the change in enthalpy (ΔH) and entropy (ΔS). It is used to determine the spontaneity of a reaction.

Conclusion

In conclusion, spontaneity is a crucial concept in chemistry that determines whether a chemical reaction will occur on its own or not. By understanding the relationship between Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS), we can determine the spontaneity of a reaction. We hope that this Q&A guide has provided you with a better understanding of spontaneity and thermodynamics.

References

  • Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
  • Chang, R. (2010). Chemistry (10th ed.). McGraw-Hill.
  • Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.

Further Reading

For further reading on spontaneity and thermodynamics, we recommend the following resources:

  • Atkins, P. W. (2007). Four laws that limit life: and how they apply to you. Oxford University Press.
  • Leach, A. G. (2005). Molecular modelling: principles and applications (2nd ed.). Prentice Hall.
  • Scott, R. A. (2010). Chemical thermodynamics: an introduction. Wiley-Blackwell.

Glossary

  • Spontaneity: The tendency of a chemical reaction to occur on its own without any external influence.
  • Gibbs free energy (ΔG): A thermodynamic property that determines the spontaneity of a reaction.
  • Enthalpy (ΔH): A thermodynamic property that determines the energy change of a reaction.
  • Entropy (ΔS): A thermodynamic property that determines the disorder or randomness of a system.