Understanding Enthalpy Change and Hess's Law

The video tutorial explains how to calculate the enthalpy change for the formation of methane from solid carbon and hydrogen gas using Hess's Law. The direct measurement of this enthalpy change is challenging due to the slow reaction rate. Instead, the enthalpy changes for the combustion of carbon, hydrogen, and methane are used. By applying Hess's Law, which states that the enthalpy change of a reaction is the sum of the enthalpy changes of its component reactions, the tutorial demonstrates how to construct the desired reaction and calculate its enthalpy change.

What is the main challenge in measuring the enthalpy change for the formation of methane directly in the laboratory?

• The reaction is too fast to measure.

• The reaction is too slow to measure.

• The reaction produces too much heat.

• The reaction requires special equipment.

Which law helps in calculating the enthalpy change for a reaction by using known enthalpies of other reactions?

• Avogadro's Law

• Hess's Law

• Charles's Law

• Boyle's Law

What is the first step in using Hess's Law to find the enthalpy change for the formation of methane?

• Measure the pressure change.

• Calculate the temperature change.

• Start with the end product.

• Start with the reactants.

When reversing a reaction, what happens to the sign of the enthalpy change?

• It remains the same.

• It becomes zero.

• It changes sign.

• It becomes positive.

Why do we multiply the enthalpy change by 2 in the hydrogen combustion reaction?

• To match the number of methane molecules.

• To match the number of oxygen molecules.

• To match the number of carbon atoms.

• To match the number of water molecules needed.

What is the enthalpy change for the combustion of carbon in graphite form?

• 0 kJ/mol

• 890.3 kJ/mol

• -393.5 kJ/mol

• -285.8 kJ/mol

What is the final enthalpy change for the formation of methane from its elements?

• 890.3 kJ/mol

• -74.8 kJ/mol

• -393.5 kJ/mol

• -571.6 kJ/mol

What type of reaction is the formation of methane from solid carbon and hydrogen gas?

• Isothermal

• Endothermic

• Neutral

• Exothermic

Which of the following is NOT a product in the reversed combustion reaction of methane?

• Carbon dioxide

• Methane

• Water

• Oxygen

What is the significance of the oxygen molecules in the reaction process?

• They are consumed and not regenerated.

• They are neither consumed nor regenerated.

• They are regenerated and not consumed.

• They are consumed and regenerated.