DE CHEM 121 Semester 1 Final Exam Review

Front

What is the formula to calculate the change in enthalpy (ΔH) for a reaction using bond energies?

Back

ΔH = Σ(Bond Energies of Reactants) - Σ(Bond Energies of Products)

Front

What is the average atomic mass of an element?

Back

The average atomic mass is calculated by multiplying the mass of each isotope by its relative abundance (as a fraction) and summing the results.

Front

How do you determine the oxidation number of an element in a compound?

Back

The oxidation number can be determined by following rules such as the oxidation state of elements in their elemental form is 0, and the sum of oxidation numbers in a neutral compound is 0.

Front

What is the balanced equation for the combustion of hydrogen?

Back

2 H₂ + O₂ → 2 H₂O

Front

How do you find the limiting reactant in a chemical reaction?

Back

The limiting reactant is the reactant that will be completely consumed first, limiting the amount of product formed. It can be found by comparing the mole ratio of reactants used in the balanced equation.

Front

What is the charge of the chromium ion in Cr₂O₇²⁻?

Back

+6 (each Cr has an oxidation state of +6 in this dichromate ion)

Front

What is the significance of bond energies in chemical reactions?

Back

Bond energies indicate the strength of bonds; higher bond energies mean stronger bonds, which require more energy to break.

Front

What is the concept of molarity in solutions?

Back

Molarity (M) is defined as the number of moles of solute per liter of solution.

Front

How do you calculate the number of moles from mass?

Back

Number of moles = mass (g) / molar mass (g/mol) of the substance.

Front

What is the principle behind the conservation of mass in chemical reactions?

Back

The principle states that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.