# Lesson Worksheet: Hess’s Law Chemistry

In this worksheet, we will practice defining and using Hess’s law to calculate enthalpy changes.

Q1:

Consider the enthalpy changes of the following reactions: Calculate the enthalpy of formation of for the given reaction:

• A kJ/mol
• B kJ/mol
• C kJ/mol
• D kJ/mol

Q2:

Consider the 3 reactions shown.

Determine the value of for the following reaction.

• A kJ/mol
• B kJ/mol
• C kJ/mol
• D

Q3:

The algebraic formula for Hessβs law is .

• A
• B
• C
• D

Q4:

The equation shows the formation of one mole of ethanol, , from its constituent elements under standard conditions and with standard states.

 Chemical Standard Enthalpy of Combustion (kJβmolβ1) Carbon, C()s Hydrogen, H2 Ethanol, CHOH()25l β394 β286 β1,371

Given the combustion values in the table, calculate the value for the standard enthalpy of formation.

Q5:

Consider the reactions shown:

What would the value of of the combustion of methane be if formed instead of ?

• A kJ/mol
• B kJ/mol
• C kJ/mol
• D kJ/mol

Q6:

Use the reactions

to calculate for the following reaction:

• A kJ/mol
• B kJ/mol
• C kJ/mol
• D kJ/mol

Q7:

By using the reactions

Calculate which refers to the heat of combustion of nitric oxide for the following reaction:

• A
• B
• C
• D

Q8:

Which of the following values is equivalent to ?

• A
• B
• C
• D
• E

Q9:

Using Hessβs law and the standard enthalpies of combustion in the given table, what is the standard enthalpy of formation of ethane, ?

 Chemical Standard Enthalpy of Combustion, (kJβmolβ1) Carbon, C()s Hydrogen, H2 Ethane, CH()26g β394 β286 β1,560

Q10:

Which of the following are necessary to have when calculating the average bond enthalpy of in a molecule of tetrachloromethane, , using Hessβs law?

1. Standard enthalpy change of atomization ()
2. Standard enthalpy change of atomization ()
3. Standard enthalpy change of formation ()
4. Standard enthalpy change of formation ()
5. Standard enthalpy change of combustion ()
6. Standard enthalpy change of combustion ()
7. Standard enthalpy change of combustion ()
• A1, 2, and 4
• B4, 5, and 6
• C1, 2, and 7
• D5, 6, and 7
• E2, 3, and 6