Given the following data: 2 O3(g) →3 O2(g) ΔH=-427 kJ O2(g) →2 O(g) ΔH=+495 kJ NO(g)

step 1 Given the following reaction, we can determine its delta H from reactions that came before it. S

Given the following data: 2 O3(g) →3 O2(g) ΔH=-427 kJ ...

Given the following data: $$\begin{aligned} 2 \mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g) & \Delta H=-427 \mathrm{kJ} \\ \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{O}(g) & \Delta H=+495 \mathrm{kJ} \end{aligned}$$ $$\mathrm{NO}(g)+\mathrm{O}_{3}(g) \rightarrow \mathrm{NO}_{2}(g)+\mathrm{O}_{2}(g)\Delta H=-199 \mathrm{kJ}$$ calculate $\Delta H$ for the reaction $$\mathrm{NO}(g)+\mathrm{O}(g) \rightarrow \mathrm{NO}_{2}(g)$$

Given the following data:
$$\begin{aligned} 2 \mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g) & \Delta H=-427 \mathrm{kJ} \\ \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{O}(g) & \Delta H=+495 \mathrm{kJ} \end{aligned}$$
$$\mathrm{NO}(g)+\mathrm{O}_{3}(g) \rightarrow \mathrm{NO}_{2}(g)+\mathrm{O}_{2}(g)\Delta H=-199 \mathrm{kJ}$$
calculate $\Delta H$ for the reaction
$$\mathrm{NO}(g)+\mathrm{O}(g) \rightarrow \mathrm{NO}_{2}(g)$$

Key Concepts

Cancellation of Intermediates

When combining multiple reactions to obtain a target reaction using Hess's Law, species that appear on both sides of the combined equations can be canceled out. This technique allows for the isolation of the reactants and products of the desired overall reaction while appropriately summing the associated enthalpy changes.

Manipulation of Thermochemical Equations

In thermochemistry, chemical equations and their corresponding enthalpy changes can be manipulated by reversing, scaling, or combining them to obtain a new reaction. When a reaction is reversed, the sign of ?H is also reversed, and when a reaction is multiplied by a coefficient, the ?H is multiplied by the same factor.

Hess's Law

Hess's Law states that the overall enthalpy change for a chemical reaction is the same, regardless of the number of steps or the pathway taken. It allows one to calculate the enthalpy change of a target reaction by algebraically adding or subtracting the enthalpy changes of other reactions that, when combined, yield the desired overall reaction.

Enthalpy Change (?H)

Enthalpy change is the heat absorbed or released under constant pressure during a chemical reaction. It is a state function, meaning its value depends only on the initial and final states of a system, not on the pathway by which the change occurs.

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