AP Chem delta G and K relationship practice questions

What does ΔG represent in thermodynamics?

ΔG represents the change in Gibbs free energy, indicating spontaneity of a reaction.

True or False: A negative ΔG indicates a non-spontaneous reaction.

False. A negative ΔG indicates that a reaction is spontaneous under standard conditions.

Fill in the blank: If ΔG = 0, the system is at _____ .

equilibrium.

What does a positive ΔG imply?

A positive ΔG implies that the reaction is non-spontaneous and requires energy input.

How is ΔG related to enthalpy and entropy?

ΔG = ΔH - TΔS, where ΔH is enthalpy change, T is temperature in Kelvin, and ΔS is entropy change.

Cause → Effect: High entropy (ΔS > 0)

Increases the favorability of a reaction, potentially leading to a negative ΔG.

What sign of ΔG indicates spontaneity at high temperatures?

A negative ΔG indicates spontaneity, especially when ΔS is positive.

Compare ΔG and equilibrium.

ΔG predicts spontaneity; at equilibrium, ΔG = 0 and the forward and reverse rates are equal.

What are standard conditions for ΔG calculations?

1 M concentrations, 1 atm pressure, and 25°C (298 K).

If ΔH is negative and ΔS is positive, what can be inferred about ΔG?

ΔG will be negative at all temperatures, indicating the reaction is always spontaneous.

True or False: ΔG is temperature dependent.

True. ΔG can change with temperature due to the $\displaystyle TΔS$ term in its equation.

What does ΔG = ΔH - TΔS tell us?

It shows how enthalpy and entropy changes influence the spontaneity of a reaction with temperature.

Define standard Gibbs free energy of formation.

The change in Gibbs free energy when one mole of a compound forms from its elements at standard conditions.

How can Gibbs free energy be useful?

It can predict the direction of a reaction, assess reaction feasibility, and calculate work obtainable.

If ΔG is zero, what can we infer about the reaction?

The system is at equilibrium, with no net change in reactants and products.

True or False: ΔG can be used to calculate equilibrium constants (K).

True. The equation ΔG° = -RT ln(K) connects ΔG to the equilibrium constant.

ΔG and K relationship definition?

The change in Gibbs free energy (ΔG) is related to the equilibrium constant (K) by the equation: ΔG° = -RT ln(K), where R is the gas constant and T is the temperature in Kelvin.

True or False: K > 1 implies a spontaneous reaction.

True. If K > 1, ΔG° is negative, indicating the reaction is spontaneous in the forward direction.

ΔG = 0 means what about K?

When ΔG = 0, the system is at equilibrium, and K = 1, meaning the concentrations of reactants and products are equal.

What does a negative ΔG indicate?

A negative ΔG indicates that the reaction is spontaneous under standard conditions and that K > 1.

At equilibrium: ΔG equals?

At equilibrium, ΔG = 0. The system has reached a state where the rate of the forward reaction equals the rate of the reverse reaction.

Fill in the blank: ΔG° = -RT ln(____)

K. This equation connects the Gibbs free energy change and the equilibrium constant.

K < 1 means what about ΔG?

If K < 1, ΔG° is positive, indicating that the reaction is non-spontaneous under standard conditions.

What is the effect of temperature on K?

Temperature changes can affect K. An increase in temperature favors endothermic reactions, increasing K for these reactions.

If K increases, what happens to ΔG?

If K increases, ΔG° becomes more negative, indicating that the reaction becomes more spontaneous.

Calculate ΔG° for: K = 1000 at 298 K.

ΔG° = -RT ln(K) = - (8.314 J/(mol·K))(298 K) ln(1000) = - 20.8 kJ/mol.

True or False: ΔG° and K are independent of reaction conditions.

False. ΔG° and K depend on temperature, pressure, and concentration of reactants/products.

Relationship of ΔG to reaction quotient Q?

ΔG = ΔG° + RT ln(Q). This equation shows how the actual free energy change relates to the reaction quotient.

When K = 1, what is ΔG°?

ΔG° = 0 when K = 1, indicating the reaction is at equilibrium.

What happens to K if ΔH is positive?

If ΔH is positive (endothermic), increasing temperature typically increases K, favoring product formation.

Effect of catalysts on K?

Catalysts do not affect K; they only speed up the rate at which equilibrium is reached.

What does a large K value indicate?

A large K value indicates a strong tendency for reactants to form products at equilibrium.

Calculate K at equilibrium: ΔG° = -40 kJ/mol?

Using ΔG° = -RT ln(K), rearranging gives K = e^(-ΔG°/RT). For -40 kJ/mol at 298 K, K ≈ 1.2 x 10^7.

How are ΔG° and K affected by pressure?

Changes in pressure can affect gaseous reactions by shifting equilibrium, indirectly affecting K.

Effect of concentration on ΔG and K?

ΔG changes with concentration shifts, but K remains constant at a given temperature.

ΔG° = -RT ln(K) relationship?

This equation connects standard Gibbs free energy change (ΔG°) to the equilibrium constant (K). Negative ΔG° indicates a forward reaction favoring products, corresponding to K > 1. Conversely, positive ΔG° suggests reactants are favored, meaning K < 1.

Calculate ΔG for a reaction at 298 K.

ΔG = ΔH - TΔS (use appropriate values).

If K > 1, what can be said about ΔG?

ΔG is negative, indicating the reaction is spontaneous under standard conditions.

True or False: ΔG° = -RT ln(K).

True. This is the standard relationship between ΔG° and K.

Fill in the blank: ΔG° = ____ at equilibrium.

0. At equilibrium, the Gibbs free energy change is zero.

Calculate K given ΔG° of -40 kJ/mol.

Use: K = e^(-ΔG°/RT). R = 8.314 J/(mol·K), T = 298 K.

Relationship: ΔG° and K.

-ΔG° = RT ln(K) - Links free energy to equilibrium.

What is the effect of increasing temperature on ΔG?

Depends on ΔH and ΔS; may decrease or increase ΔG.

If ΔH is positive and ΔS is negative, what can be said about ΔG?

ΔG is always positive; reaction non-spontaneous at all temperatures.

Determine K from ΔG° = +25 kJ/mol.

K < 1, indicates non-spontaneous reaction at standard state.

Calculate ΔG at 1000 K if ΔH = 200 kJ and ΔS = 300 J/K.

ΔG = 200,000 J - 1000 J/K × 1000 K = -800,000 J.

True or False: A large K value means ΔG is positive.

False. A large K value means ΔG is negative.

How does pressure affect ΔG for gas reactions?

Increased pressure shifts equilibrium, potentially lowering ΔG.

Calculate K when ΔG° = -57.2 kJ/mol.

K = e^(ΔG°/(-RT)), K = e^(57,200/(8.314 × 298)).

Effect of ΔS on ΔG at high temperatures.

Higher ΔS values decrease ΔG, potentially making reactions spontaneous.

When is ΔG negative?

When K > 1 and the reaction proceeds forward spontaneously.

Determine ΔG at 298 K if ΔH = -100 kJ and ΔS = -200 J/K.

ΔG = -100,000 J + 298 × -200 J/K = +59,600 J.

What does a small K value imply about the equilibrium position?

The equilibrium favors reactants, indicating a non-spontaneous forward reaction.

Fill in the blank: ΔG° < 0 implies _____.

K > 1, favors products.

Example: If ΔH = -50 kJ and ΔS = 150 J/K, at what T is ΔG = 0?

0 = -50,000 + T(150); T = 333.3 K.

Calculate ΔG at 298 K for K = 0.01.

Use the formula: ΔG° = -RT ln(K). R = 8.314 J/(mol·K), T = 298 K. ΔG° = - (8.314 J/(mol·K) * 298 K) * ln(0.01) = 12.76 kJ/mol.