Enthalpy Changes Flashcards

Questions and Answers

What is enthalpy defined as?

Measure of heat energy present in a chemical reaction (correct)

The pressure of a gas

A measure of temperature in reactions

None of the above

What is enthalpy change?

Amount of energy released/taken in during a chemical reaction (cannot be measured)

An exothermic reaction releases energy into its surroundings.

True

What is the symbol for an exothermic reaction?

-∆H Signup and view all the answers

An endothermic reaction releases energy from its surroundings.

False Signup and view all the answers

What is the symbol for an endothermic reaction?

+∆H Signup and view all the answers

What is activation energy?

Minimum energy required for a reaction to take place Signup and view all the answers

What is the symbol for enthalpy change under standard conditions?

∆H^θ Signup and view all the answers

What are the standard conditions in chemistry?

100kPa, 298K and the standard state of the substance Signup and view all the answers

What is enthalpy change of reaction?

Enthalpy change for a reaction when molar quantities of reactants react together Signup and view all the answers

What is enthalpy change of formation?

Enthalpy change associated with the formation of 1 mole of a compound from its elements Signup and view all the answers

What is enthalpy change of combustion?

Enthalpy change associated with the complete combustion of 1 mole of substance Signup and view all the answers

What is the enthalpy change of neutralization?

Enthalpy change associated with the formation of 1 mole of water from a neutralisation reaction between acid and base Signup and view all the answers

What is the ionic equation for all strong base and strong acid reactions?

H⁺ + OH⁻ = H₂O Signup and view all the answers

What is the enthalpy change of neutralization for strong acids and bases?

∆neutH = -57 Signup and view all the answers

How is ∆neutH calculated?

q / moles of water Signup and view all the answers

What is the calculation rule for enthalpy change reactions?

Bond breaking - bond making Signup and view all the answers

What is the formula to calculate enthalpy change of formation?

∆H2 - ∆H1 Signup and view all the answers

What is the formula to calculate enthalpy change of combustion?

∆H1 - ∆H2 Signup and view all the answers

Bond breaking is endothermic.

True Signup and view all the answers

Bond making is exothermic.

True Signup and view all the answers

How is Delta H calculated?

Products - reactants Signup and view all the answers

Study Notes

Enthalpy Concepts

Enthalpy measures the heat energy involved in a chemical reaction.
Enthalpy change quantifies the energy released or absorbed during a reaction and cannot be directly measured.
Exothermic reactions release energy to the surroundings, indicated by a negative enthalpy change symbol (-∆H).
Endothermic reactions absorb energy from the surroundings, denoted by a positive enthalpy change symbol (+∆H).

Activation Energy

Activation energy is the minimum energy needed to initiate a reaction, primarily to break bonds.

Standard Conditions

Enthalpy change under standard conditions is represented as ∆H^θ.
Standard conditions include a pressure of 100 kPa, a temperature of 298 K, and the standard state of a substance (e.g., O₂ as a gas).

Types of Enthalpy Change

Enthalpy change of reaction refers to the change occurring when molar quantities of reactants react together.
Enthalpy change of formation is the change related to forming one mole of a compound from its elements.
Enthalpy change of combustion involves the complete combustion of one mole of a substance.
The enthalpy change of neutralization refers to the formation of one mole of water from a neutralization reaction between an acid and a base.

Neutralization Reactions

The ionic equation for reactions between strong acids and bases is H⁺ + OH⁻ = H₂O.
Since all strong acid-base reactions have the same ionic equation, the enthalpy change of neutralization is consistently -57 kJ/mol.

Calculating Enthalpy Changes

To calculate the enthalpy change of neutralization (∆neutH), use the formula q (heat absorbed/released) divided by the moles of water produced.
The general rule for calculating enthalpy changes in reactions is bond breaking - bond making, remembering to consider the signs.
The formula to calculate enthalpy change of formation is ∆H2 - ∆H1.
The formula for enthalpy change of combustion is ∆H1 - ∆H2.

Bond Energy

Bond breaking is associated with an endothermic process, which requires energy input.
Bond making is exothermic, releasing energy during bond formation.

Delta H Calculation

The change in enthalpy (ΔH) is determined by subtracting the total energy of reactants from the total energy of products, resulting in either a positive or negative value.

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Description

Explore the fundamental concepts of enthalpy changes in chemical reactions through these flashcards. Each card provides a key term and its definition, aiding in the understanding of exothermic reactions and enthalpy calculations.