Revision of Chemical Energetics

What is the definition of enthalpy change?

• The change in volume of a system at constant temperature

• The change in color of a system during a reaction

• The heat absorbed or released by a system at constant pressure.

• The change in mass of a system during a reaction

State Hess's Law and its significance in chemical energetics.

• Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the route taken. It is significant in chemical energetics because it allows us to calculate the overall enthalpy change of a reaction using known enthalpy changes of other reactions.

• Hess's Law states that the total enthalpy change for a reaction depends on the route taken.

• Hess's Law is not significant in chemical energetics and has no practical use.

• Hess's Law only applies to exothermic reactions and not endothermic reactions.

Explain the concept of bond enthalpy and how it relates to chemical reactions.

• The number of bonds and its relation to the overall energy change in a reaction.

• The length of the bond and its relation to the overall energy change in a reaction.

• The energy required to break a chemical bond and its relation to the overall energy change in a reaction.

• The color of the bond and its relation to the overall energy change in a reaction.

Describe the process of calorimetry and its role in determining energy changes in chemical reactions.

• Calorimetry is used to measure the color changes in chemical reactions by determining the heat released or absorbed.

• Calorimetry is a method used to measure the pressure changes in chemical reactions by determining the heat released or absorbed.

• Calorimetry is used to measure the energy changes in chemical reactions by determining the heat released or absorbed.

• Calorimetry is a process used to measure the volume changes in chemical reactions by determining the heat released or absorbed.

What is the standard enthalpy of formation and how is it used in chemical energetics?

• It is the change in enthalpy when one mole of a substance is formed from its elements in their standard states, and it is used to calculate the heat of reaction and determine the stability of a compound.

• It is the change in enthalpy when one mole of a substance is formed from its elements in their non-standard states, and it is used to calculate the heat of fusion and determine the stability of a compound.

• It is the change in entropy when one mole of a substance is formed from its elements in their standard states, and it is used to calculate the mass of a compound.

• It is the change in enthalpy when one mole of a substance is decomposed into its elements in their standard states, and it is used to calculate the heat of vaporization and determine the stability of a compound.

Calculate the enthalpy change for the reaction: 2H2(g) + O2(g) -> 2H2O(l) given the standard enthalpies of formation.

• The enthalpy change for the reaction is -1000 kJ

• The enthalpy change for the reaction is -483.6 kJ

• The enthalpy change for the reaction is 200 kJ

• The enthalpy change for the reaction is 0 kJ

Using Hess's Law, calculate the enthalpy change for the reaction: C(s) + O2(g) -> CO2(g) given the following equations: 2C(s) + 3H2(g) -> C2H6(g) and C2H6(g) + 7/2O2(g) -> 2CO2(g) + 3H2O(l)

• -560 kJ

• -1560 kJ

• -2560 kJ

• 0 kJ

Determine the enthalpy change for the reaction: N2(g) + 3H2(g) -> 2NH3(g) using bond enthalpies.

• The enthalpy change for the reaction is -92 kJ/mol.

• The enthalpy change for the reaction is -50 kJ/mol.

• The enthalpy change for the reaction is 0 kJ/mol.

• The enthalpy change for the reaction is +92 kJ/mol.

A student conducts an experiment to determine the enthalpy change for the reaction: Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g). If the student measures a temperature increase of 15°C in the reaction mixture, calculate the enthalpy change.

• The enthalpy change for the reaction is calculated to be ΔH = q/m, where q = mcΔT and m is the mass of the reactants.

• The enthalpy change for the reaction is calculated to be ΔH = q/n, where q = mcΔT and n is the number of moles of the limiting reactant.

• The enthalpy change for the reaction is calculated to be ΔH = q/n, where q = mcΔT and n is the number of moles of the product formed.

• The enthalpy change for the reaction is calculated to be ΔH = q/n, where q = mcΔT and n is the number of moles of the excess reactant.

Explain how the enthalpy change of a reaction can be used to predict the feasibility of a chemical process.

• By comparing the enthalpy change to the molecular weight of the reactants and products.

• By comparing the enthalpy change to the solubility of the reactants and products.

• By comparing the enthalpy change to the standard enthalpy of formation for the reactants and products.

• By comparing the enthalpy change to the color of the reactants and products.