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Chemistry Chapter: Thermodynamics

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Questions and Answers

What characterizes an endothermic reaction?

The enthalpy change is negative.

Heat is absorbed from the surroundings. (correct)

Bond energies are always greater than bond dissociation energies.

Heat is released to the surroundings.

Which reaction has the highest enthalpy change based on the provided examples?

N₂(g) + O₂(g) → 2NO(g) ΔH° = +180.5 kJ (correct)

C(s) + H₂O(g) → CO(g) + H₂(g) ΔH° = +131.4 kJ

H₂(g) + O₂(g) → H₂O(l) ΔH° = -285.8 kJ

H₂(g) + I₂(g) → 2HI(g) ΔH° = +53.8 kJ

What is the relationship between bond energy and bond dissociation energy?

Bond energy is always greater than bond dissociation energy.

Bond dissociation energy is related to forming bonds.

Bond dissociation energy requires energy to break bonds. (correct)

There is no relationship between the two.

How is the standard enthalpy change, ΔH°, defined?

<p>It is the enthalpy change at standard conditions of 1 atm and 25°C.</p> Signup and view all the answers

What determines whether a reaction absorbs or releases energy?

<p>The difference between bond energies and bond dissociation energies.</p> Signup and view all the answers

Study Notes

Endothermic Reactions

Endothermic reactions absorb heat from the surroundings
Heat is transferred from the surroundings to the system
Examples include the decomposition of limestone, the sublimation of dry ice, and the freezing of water

Exothermic Reactions

Exothermic reactions release heat into the surroundings
Heat is transferred from the system to the surroundings
Examples include the combustion of methane and the freezing of water

Enthalpy of Reaction

Enthalpy of reaction is the amount of heat absorbed or released during a chemical reaction
Measured at 25°C (or 298K) and one atmospheric pressure
Negative for exothermic reactions
Positive for endothermic reactions

Bond Energy

Breaking bonds requires energy
Forming bonds releases energy
Bond dissociation energy = energy to break one mole of a particular bond
Bond energy = energy released when forming one mole of a bond

Enthalpy Change (ΔH°)

ΔH° = Sum of bond dissociation energies of reactants - Sum of bond energies of products
It indicates whether the reaction absorbs or releases energy

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Description

This quiz covers key concepts in thermodynamics, focusing on endothermic and exothermic reactions, enthalpy of reaction, and bond energy. You will learn how heat transfer affects chemical processes and the implications of bond energy in thermodynamic calculations.