Calculating Enthalpy of Reaction

These flashcards cover key concepts, equations, and definitions related to the calculation of enthalpy of reactions as discussed in the lecture notes.

What are the four ways to calculate the enthalpy of a chemical reaction?

1. Calorimetry 2. Bond Enthalpies 3. Enthalpies of Formation 4. Hess’s Law.

What must be true according to the first law of thermodynamics?

The heat lost by the system must equal the heat gained by the surroundings.

In calorimetry, how is the enthalpy of a reaction calculated?

ΔHreaction = qreaction/molesrxn.

What is the standard enthalpy of formation, ΔH°f?

The change in energy when one mole of a compound is formed from its elements in their standard states.

For which conditions is ΔH°f equal to zero?

For elements in their standard states.

How do you calculate ΔH°rxn using standard enthalpies of formation?

ΔH°rxn = Σ(ΔH°f of products) - Σ(ΔH°f of reactants).

What is bond enthalpy?

The energy required to break a bond.

What does it mean when a reaction is endothermic?

Energy is absorbed, and the energy required for breaking bonds is greater than the energy released when forming bonds.

What happens to the reaction when the enthalpy change is negative?

Energy is released when the reaction occurs.

Describe Hess's Law.

If a reaction can be described as a series of steps, then the ΔH for the overall reaction is the sum of the ΔH values for each step.

In a calorimeter, what is measured to find heat changes?

The temperature change of the solution.

What factors influence whether a reaction is classified as exothermic or endothermic?

Comparison of the energy required to break bonds versus the energy released in forming bonds.

What equipment is used to measure heat changes in chemistry?

A calorimeter.

What is calorimetry primarily used for?

To determine the calorific value of foods and heat changes in chemical reactions.

How is enthalpy change related to stoichiometry?

Stoichiometry allows the calculation of ΔHrxn based on the amounts of substances reacting.

What does a negative ΔH°f indicate about a reaction?

Energy is released when the compound is formed from its elements.

How do you determine heat evolution in a neutralization reaction?

By measuring the temperature change and using specific heat calculations.