Enthalpy, entropy, Gibbs free energy, and the laws of thermodynamics as applied to chemical reactions tested on the MCAT.
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- What does the first law of thermodynamics state?
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Energy cannot be created or destroyed, only transformed or transferred- What is the formula for the change in internal energy according to the first law of thermodynamics?
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Delta U = Q - W (heat added minus work done by the system)- What does enthalpy (H) represent?
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The heat content of a system at constant pressure- What is the sign of the enthalpy change in an exothermic reaction?
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Negative- What is the sign of the enthalpy change in an endothermic reaction?
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Positive- What law states that the total enthalpy change of a reaction is the same whether it occurs in one step or multiple steps?
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Hess's law- What does entropy (S) measure?
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The degree of disorder or randomness in a system- What does the second law of thermodynamics state about the entropy of an isolated system?
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The entropy of an isolated system tends to increase over time- What does the third law of thermodynamics state about a perfect crystal at absolute zero?
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Its entropy is exactly zero- What is the formula for Gibbs free energy in terms of enthalpy, entropy, and temperature?
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Delta G = Delta H - T(Delta S)- What does a negative Gibbs free energy (Delta G < 0) indicate about a reaction?
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The reaction is spontaneous under the given conditions- What does a positive Gibbs free energy (Delta G > 0) indicate about a reaction?
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The reaction is nonspontaneous under the given conditions- Under what condition of Gibbs free energy is a reaction at equilibrium?
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Delta G = 0- How does temperature affect spontaneity when Delta H is positive and Delta S is positive?
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The reaction becomes spontaneous at high temperatures- What thermodynamic quantity describes the heat required to raise the temperature of a substance by one degree?
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Heat capacity
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