Practice Problem: Hess's Law

The video tutorial explains how to use Hess's Law to calculate the change in enthalpy for a given reaction. It involves manipulating given thermochemical equations by adjusting stoichiometric coefficients and flipping equations to align reactants and products. The tutorial guides through the process of ensuring all unwanted substances cancel out, leaving the desired reaction. Finally, it demonstrates how to sum the adjusted enthalpy values to find the overall Delta H for the reaction.

What is the main goal when using Hess's Law in this problem?

• To find the unknown delta H value for a given reaction.

• To balance chemical equations.

• To determine the molecular weight of compounds.

• To calculate the rate of reaction.

How do you adjust the stoichiometry of the first equation to match the desired reaction?

• Remove all products from the equation.

• Cut all coefficients and delta H in half.

• Double all coefficients and delta H.

• Add more reactants to the equation.

What is the necessary manipulation for the second equation to obtain F2 as a reactant?

• Add F2 to the reactants.

• Double the amount of F2.

• Flip the equation and cut it in half.

• Remove F2 from the products.

What happens to the delta H value when you flip an equation?

• The sign is reversed.

• It doubles.

• It remains the same.

• It is divided by two.

How is the third equation manipulated to make CLF3 a product?

• By removing CLF3 from the products.

• By adding more CLF3 to the reactants.

• By doubling the amount of CLF3.

• By flipping the equation.

What is the final step after ensuring all unwanted components cancel out?

• Recalculate the molecular weights.

• Add up the adjusted delta H values.

• Rebalance the chemical equation.

• Determine the reaction rate.

What is the final delta H value for the reaction in question?

• -266.7 kJ

• 24.7 kJ

• 102.8 kJ

• -139.2 kJ