Energy Changes in Chemical Reactions - SS1 Chemistry Past Questions and Answers - page 4
Define heat of formation and explain how it is related to enthalpy changes and Hess's Law.
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Which of the following best defines spontaneity in a chemical reaction?
The reaction occurs rapidly.
The reaction occurs without any external influence.
The reaction occurs with a decrease in entropy.
The reaction occurs at a constant temperature.
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Spontaneous reactions are characterised by:
A positive change in Gibbs free energy (ΔG).
A negative change in Gibbs free energy (ΔG).
A zero change in Gibbs free energy (ΔG).
An unpredictable change in Gibbs free energy (ΔG).
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Which of the following statements is true regarding the Gibbs free energy (ΔG) of a spontaneous reaction?
ΔG is always positive.
ΔG is always negative.
ΔG can be positive or negative depending on the reaction conditions.
ΔG is always zero.
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The relationship between the change in Gibbs free energy (ΔG), enthalpy change (ΔH), and entropy change (ΔS) is given by:
ΔG = ΔH + ΔS
ΔG = ΔH - ΔS
ΔG = ΔH/ΔS
ΔG = ΔS/ΔH
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Which of the following conditions indicates that a reaction is spontaneous at all temperatures?
ΔH > 0 and ΔS > 0
ΔH < 0 and ΔS < 0
ΔH > 0 and ΔS < 0
ΔH < 0 and ΔS > 0
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The spontaneity of a reaction can be determined by:
The initial concentrations of reactants.
The activation energy of the reaction.
The sign of ΔG.
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At equilibrium, the value of ΔG for a reaction is:
Negative
Zero
Cannot be determined
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Which of the following conditions indicates a non-spontaneous reaction?
ΔG = 0
ΔG < 0
ΔG > 0
ΔG is not defined for non-spontaneous reactions.
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The spontaneity of a reaction can be determined by comparing:
Activation energy with enthalpy change.
Enthalpy changes with entropy change.
Gibbs free energy change with activation energy.
Entropy changes with activation energy.
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