Enthalpy Changes in Reactions

The video tutorial explains the concepts of standard enthalpy change of formation and combustion. It defines the enthalpy change of formation as the energy change when one mole of a substance is formed from its elements under standard conditions. An example calculation is provided using propane combustion. The tutorial then introduces the enthalpy change of combustion, defined as the energy change when one mole of a substance burns completely in oxygen. Another example calculation is demonstrated using ethane reaction. Key differences between formation and combustion calculations are highlighted.

What is the standard enthalpy change of formation?

• The energy change when one mole of a substance dissolves in water.

• The energy change when one mole of a substance burns completely in oxygen.

• The energy change when one mole of a substance is converted to gas.

• The energy change when one mole of a substance is formed from its elements in their standard states.

Under what conditions are standard enthalpy changes measured?

• 273K and 1 atm

• 300K and 1 atm

• 298K and 101.3 kPa

• 273K and 100 kPa

Why do free elements like oxygen and hydrogen have a standard enthalpy change of formation value of zero?

• Because they do not react with other elements.

• Because they have high energy content.

• Because they are gases at room temperature.

• Because they are already in their standard states.

In the example of propane combustion, what is the standard enthalpy change of formation for carbon dioxide?

• 0 K per mole

• -105 K per mole

• -286 K per mole

• -394 K per mole

How is the overall enthalpy change calculated using standard enthalpy of formation values?

• Sum of reactants minus sum of products

• Sum of products minus sum of reactants

• Sum of reactants plus sum of products

• Sum of products plus sum of reactants

What is the definition of standard enthalpy change of combustion?

• The energy change when one mole of a substance is formed from its elements.

• The energy change when one mole of a substance burns completely in oxygen.

• The energy change when one mole of a substance is converted to gas.

• The energy change when one mole of a substance dissolves in water.

How does the calculation of enthalpy change differ between formation and combustion?

• Both use products minus reactants.

• Both use reactants minus products.

• Formation uses products minus reactants, combustion uses reactants minus products.

• Formation uses reactants minus products, combustion uses products minus reactants.

In the example of ethane reacting with hydrogen, what is the standard enthalpy change of combustion for hydrogen?

• 1560 K per mole

• 0 K per mole

• -286 K per mole

• -1411 K per mole

What is the overall enthalpy change for the reaction of ethane with hydrogen using standard enthalpy changes of combustion?

• -1560 K per mole

• 1560 K per mole

• -137 K per mole

• 137 K per mole

Which side of the reaction equation are the reactants located when calculating enthalpy change of combustion?

• Right side of the arrow

• Left side of the arrow

• Above the arrow

• Below the arrow