Thermodynamics Quiz

Exothermic Reactions

• Exothermic reactions release heat energy, resulting in an increase in temperature of the surroundings.
• Common examples include combustion reactions.

Entropy and Reactions

• Reactions that increase entropy (S) tend to disperse energy and matter, leading to a more disorderly system.
• Increasing entropy is associated with processes like mixing, phase changes from solid to liquid, or gas formation.

Gibbs Free Energy (ΔG)

• A negative ΔG indicates a spontaneous reaction, meaning it can occur without external input.
• A positive ΔG suggests a non-spontaneous reaction, requiring energy to proceed.

Reaction Equilibrium

• A reaction is at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction, resulting in constant concentrations of reactants and products.

Non-Standard Conditions

• A reaction is considered under non-standard conditions when reactants and products are at concentrations other than 1 M, and/or when temperature is not 25°C or pressure is not 1 atm.

Gibbs Free Energy and Concentration Changes

• Increasing reactants compared to products typically lowers ΔG, favoring the formation of products.
• Reducing reactants compared to products raises ΔG, making the formation of products less favorable.

ATP Phosphorylation

• Phosphorylation of ATP occurs to store energy in high-energy phosphate bonds, serving as a key energy currency for cellular processes.

Enzyme Function

• Enzymes do not affect ΔG directly; they lower the activation energy, speeding up the rate of reaction without altering the energy change.

Thermodynamics Systems

• A closed system can exchange energy but not matter with its surroundings, ideal for studying changes without mass loss.
• An open system allows both energy and matter to be exchanged, typical in biological environments.

First Law of Thermodynamics

• The first law states energy is conserved; it cannot be created or destroyed, only transformed, during a chemical change.

Enthalpy (ΔH)

• Enthalpy refers to the total energy of a system, including internal energy and pressure-volume work.
• ΔH is measured by the heat absorbed or released under constant pressure during a reaction.

Enthalpy Change Values

• ΔH for exothermic reactions is negative, indicating heat is released.
• ΔH for endothermic reactions is positive, indicating heat is absorbed.
• Isothermal reactions have ΔH equal to zero, where temperature remains constant.

Second Law of Thermodynamics

• The second law states the total entropy of the universe tends to increase over time, leading systems toward disorder.

Spontaneity Conditions

• An increase in entropy (positive ΔS) can offset a positive ΔH, potentially allowing a spontaneous reaction.
• A negative ΔS with a positive ΔH can also lead to spontaneity under specific conditions.
• A reaction will never be spontaneous if both ΔH is positive and ΔS is negative.
• If product concentration exceeds reactant concentration, the reaction is less likely to proceed forward.
• A reaction will always be spontaneous if ΔG is negative.