Recalling Enthalpy Changes

What is the difference between exothermic and endothermic reactions?

• Exothermic reactions do not involve energy changes; endothermic reactions do.

• Exothermic reactions absorb energy; endothermic reactions release energy.

• Exothermic reactions release energy; endothermic reactions absorb energy.

• Exothermic reactions are always spontaneous; endothermic reactions are not.

How do you calculate the change in enthalpy for a reaction?

• ΔH = ΣH(products) - ΣH(reactants)

• ΔH = H(products) - H(reactants)

• ΔH = H(reactants) + H(products)

• ΔH = H(products) / H(reactants)

How can you determine the enthalpy change using bond enthalpies?

• ΔH = Σ(bond enthalpies of all bonds)

• ΔH = Σ(bond enthalpies of reactants) - Σ(bond enthalpies of products)

• ΔH = Σ(bond enthalpies of formed bonds) - Σ(bond enthalpies of broken bonds)

• ΔH = Σ(bond enthalpies of broken bonds) - Σ(bond enthalpies of formed bonds)

What is the significance of the enthalpy change in chemical reactions?

• Enthalpy change only affects the temperature of the reaction.

• Enthalpy change is irrelevant to reaction rates.

• Enthalpy change is significant as it reveals whether a reaction is exothermic or endothermic, influencing energy dynamics and spontaneity.

• Enthalpy change determines the color of the products.

What role does enthalpy play in predicting the spontaneity of a reaction?

• Enthalpy is only relevant for gas-phase reactions.

• Enthalpy change can indicate whether a reaction is favorable under constant temperature and pressure.

• Enthalpy change is irrelevant in determining reaction mechanisms.

• Enthalpy does not influence spontaneity; only entropy matters.

How does temperature affect the enthalpy change of a reaction?

• Temperature has no effect on enthalpy change.

• Higher temperatures always increase enthalpy change.

• Enthalpy change can vary with temperature due to changes in heat capacity.

• Temperature only affects the enthalpy of gaseous reactants.

Draw a well-labelled energy profile diagram to represent an EXOTHERMIC reaction.

What is the sign (+ or -) of an Endothermic reaction?

• +, Positive

• -, Negative

• There is no need to indicate any signs.