Chemical Energetics

When iron reacts with oxygen to form rust, heat is slowly released. This is an example of:

Which statement is true regarding the energy of bonds?

Which of the following processes is exothermic?

Which observation indicates an endothermic reaction is occurring in a beaker?

Why is the reaction between an acid and an alkali considered exothermic?

Which statement correctly describes an endothermic reaction?

If $100\ kJ$ of energy is needed to break the bonds in the reactants and $80\ kJ$ of energy is released when the bonds in the products are formed, what is the $\Delta H$ of the reaction?

A reaction pathway shows a very high activation energy and a very large negative enthalpy change. What can be concluded about this reaction?

If the enthalpy of neutralization for a strong acid and a strong base is $-57\ kJ/mol$, why is the enthalpy of neutralization for ethanoic acid (a weak acid) and sodium hydroxide slightly less exothermic (e.g., $-54\ kJ/mol$)?

The average bond energy of $C-H$ is $413\ kJ/mol$. Which statement correctly describes this value?

If a reaction has a very high activation energy as shown in the diagram, it is likely to be:

What does the peak of the curve in an energy level diagram represent?

Which transition in the diagram represents a process where $\Delta H$ is positive?

In an energy level diagram, what does the horizontal axis usually represent?

In the context of the Boltzmann distribution and energy level diagrams, what happens to the number of molecules able to cross the activation energy barrier when temperature increases?

Which of the following would change the position of the product line relative to the reactant line in an energy level diagram?

Using the diagram, determine which step is the rate-determining step in this two-step reaction.

A graph of Potential Energy vs Reaction Coordinate shows a reaction where the bond-breaking step requires $600\text{ kJ mol}^{-1}$ and the bond-forming step releases $750\text{ kJ mol}^{-1}$. If the reactants start at an energy of $200\text{ kJ mol}^{-1}$, identify the correct coordinates $(x, y)$ for the transition state and the products, assuming the transition state occurs at $x=5$ and products at $x=8$.

A biological enzyme facilitates the reaction $S \rightarrow P$. In the absence of the enzyme, the energy profile shows an activation energy of $85\text{ kJ mol}^{-1}$. With the enzyme, the reaction follows a different mechanism with two smaller peaks ($E_{a1} = 20\text{ kJ mol}^{-1}$ and $E_{a2} = 15\text{ kJ mol}^{-1}$ relative to the intermediate). If the intermediate is $10\text{ kJ mol}^{-1}$ below the reactants, what is the total reduction in the 'energy barrier' to reach the highest point of the pathway compared to the uncatalyzed reaction?

An explorer finds that a portable heater uses the reaction $M + O_2 \rightarrow MO_2$. The energy level diagram shows that the enthalpy of the reactants is $H_R$ and the enthalpy of the products is $H_P$. If the magnitude of the enthalpy change $|\Delta H|$ is $480\text{ kJ mol}^{-1}$ and the energy of the transition state is $120\text{ kJ mol}^{-1}$ above the reactants, what is the ratio of $E_a(\text{forward})$ to $E_a(\text{reverse})$ for this exothermic process?

Which of these bonds requires the least energy to break based on their bond energies? $C-H = 413$, $C-C = 348$, $O-H = 463$, $H-Cl = 431$.

How many $C-H$ bonds are broken in the reaction of $1$ mole of ethane ($C_{2}H_{6}$)?

A reaction has a total bond breaking energy of $1500\text{ kJ}$ and a total bond forming energy of $1400\text{ kJ}$. The reaction is:

In an exothermic reaction, where does the 'extra' energy come from?

Calculate the enthalpy change for the formation of 1 mole of water vapor from its elements: $H_{2} + 0.5O_{2} \rightarrow H_{2}O$. Bond energies: $H-H = 436, O=O = 496, O-H = 463$.

Calculate the $\Delta H$ for: $C_{2}H_{6} + 3.5 O_{2} \rightarrow 2CO_{2} + 3H_{2}O$. Bond energies: $C-C = 347, C-H = 413, O=O = 496, C=O = 805, O-H = 463$.

Which reaction releases more energy per mole of reactant? Reaction 1: $H_{2} + Cl_{2} \rightarrow 2HCl$ ($\Delta H = -184\text{ kJ/mol}$) Reaction 2: $H_{2} + F_{2} \rightarrow 2HF$ ($\Delta H = -542\text{ kJ/mol}$)

Based on the enthalpy of the reaction $2H_{2} + O_{2} \rightarrow 2H_{2}O$ being $-484\text{ kJ/mol}$ and the bond energies $H-H = 436$ and $O=O = 498$, what is the bond energy of the $O-H$ bond?

Calculate the enthalpy change for the hydration of propene: $CH_{3}CH=CH_{2} + H_{2}O \rightarrow CH_{3}CH(OH)CH_{3}$. Bond energies: $C=C = 614$, $C-C = 347$, $C-H = 413$, $O-H = 464$, $C-O = 358$.

For the reaction $SF_{4} + F_{2} \rightarrow SF_{6}$, calculate $\Delta H$. Assume $S-F$ average bond energy is $327\text{ kJ/mol}$ and $F-F$ is $158\text{ kJ/mol}$.