Hess's Law and Heats of Formation

The video tutorial explains Hess's Law and how thermochemical equations can be manipulated to calculate the enthalpy change (delta H) of chemical reactions. It covers two methods: manipulating equations and using standard enthalpies of formation. The tutorial provides rules for equation manipulation and demonstrates an example using Hess's Law. It also explains the concept of standard enthalpies of formation and how to use them to calculate delta H. The video concludes with a comprehension check.

What is the primary purpose of using thermochemical equations in chemical reactions?

• To determine the color change in reactions

• To predict the energy absorbed or released

• To calculate the speed of the reaction

• To find the mass of reactants

According to Hess's Law, what happens to delta H when a reaction is reversed?

• It remains the same

• It becomes zero

• It doubles

• It changes sign

When coefficients in a thermochemical equation are multiplied, what happens to delta H?

• It is divided by the same factor

• It remains unchanged

• It is subtracted by the same factor

• It is multiplied by the same factor

What does the standard state refer to in the context of standard enthalpies of formation?

• High temperature and pressure

• Low temperature and pressure

• Room temperature and atmospheric pressure

• Zero temperature and pressure

How is the change in enthalpy for a reaction calculated using standard heats of formation?

• By multiplying the heats of formation of reactants and products

• By adding the heats of formation of reactants and products

• By subtracting the heats of formation of reactants from products

• By subtracting the heats of formation of products from reactants