Hess's Law and Enthalpy Changes

In this video tutorial, Melissa Maribel explains a common type of Hess's Law question often seen on tests. The tutorial guides viewers through manipulating three given reactions to achieve a goal reaction, focusing on adjusting reactants and products, multiplying reactions, and flipping reactions to ensure they are on the correct side. The tutorial concludes with combining and simplifying reactions to find the total enthalpy change. Melissa also introduces another challenging Hess's Law question for further practice.

What is the primary objective when using Hess's Law in this tutorial?

• To calculate the mass of reactants.

• To find the change in enthalpy of a given reaction.

• To balance chemical equations.

• To determine the rate of a reaction.

What is the first step in manipulating a reaction according to Hess's Law?

• Reversing the reaction.

• Multiplying the reaction by a number.

• Identifying the reactants and products.

• Adjusting the temperature.

When adjusting the quantity of carbon in a reaction, what must also be adjusted?

• The volume of the reaction.

• The temperature of the reaction.

• The enthalpy change of the reaction.

• The pressure of the reaction.

How do you adjust the quantity of H2 in a reaction?

• By altering the pressure.

• By adding more H2 to the reaction.

• By multiplying the entire reaction by a specific number.

• By changing the temperature.

What happens to the enthalpy change when a reaction is reversed?

• It is divided by 2.

• It remains the same.

• It is multiplied by 2.

• It is multiplied by -1.

What is the result of summing up all reactions and enthalpy changes?

• The mass of the products.

• A balanced chemical equation.

• The total enthalpy change of the goal reaction.

• The rate of the reaction.

Why is it important to check the side of the reactants and products in a reaction?

• To ensure the reaction is balanced.

• To determine the reaction rate.

• To ensure they are on the correct side for the goal reaction.

• To calculate the mass of the reactants.

What must be done if the product is on the wrong side of the reaction?

• Reverse the reaction.

• Add more reactants.

• Increase the temperature.

• Decrease the pressure.

What should be done with like terms in the final reaction?

• They should be ignored.

• They should be halved.

• They should be combined and canceled out.

• They should be doubled.

What is the significance of the goal reaction in this tutorial?

• It is an intermediate step.

• It is the starting point of the process.

• It is used to determine the reaction rate.

• It is the final reaction with the desired enthalpy change.