Given the data N2(g)+O2(g) ⟶2 NO(g) ΔH=+180.7 kJ 2 NO(g)+O2(g) ⟶2 NO2(g) ΔH=-113.1 kJ

Given the data N2(g)+O2(g) ⟶2 NO(g) ΔH=+180.7 kJ 2...

Given the data $$\begin{aligned} \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g) & \Delta H=+180.7 \mathrm{kJ} \\ 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) & \Delta H=-113.1 \mathrm{kJ} \\ 2 \mathrm{N}_{2} \mathrm{O}(g) \longrightarrow 2 \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) & \Delta H=-163.2 \mathrm{kJ} \end{aligned}$$ use Hess's law to calculate $\Delta H$ for the reaction $$\mathrm{N}_{2} \mathrm{O}(g)+\mathrm{NO}_{2}(g) \longrightarrow 3 \mathrm{NO}(g)$$

Given the data
$$\begin{aligned} \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g) & \Delta H=+180.7 \mathrm{kJ} \\ 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) & \Delta H=-113.1 \mathrm{kJ} \\ 2 \mathrm{N}_{2} \mathrm{O}(g) \longrightarrow 2 \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) & \Delta H=-163.2 \mathrm{kJ} \end{aligned}$$
use Hess's law to calculate $\Delta H$ for the reaction
$$\mathrm{N}_{2} \mathrm{O}(g)+\mathrm{NO}_{2}(g) \longrightarrow 3 \mathrm{NO}(g)$$

Key Concepts

Hess's Law

This principle states that the total enthalpy change for a chemical reaction is the same, regardless of the path taken from reactants to products. Because enthalpy is a state function, individual steps may be added, subtracted, or reversed, and the overall enthalpy change will always be the sum of the changes for the individual steps.

Enthalpy as a State Function

Enthalpy is a thermodynamic quantity that depends only on the current state of a system, not on how that state was reached. This key concept means that when combining multiple chemical reactions, their enthalpy changes can be algebraically added to obtain the enthalpy change for the overall reaction.

Manipulation of Chemical Equations

In applying Hess's Law, chemical equations can be reversed or multiplied by a scalar to match the desired overall reaction. When reactions are reversed, the sign of their enthalpy change must also be reversed, and when a reaction is multiplied by a number, its enthalpy change must be multiplied by the same number. This manipulation is essential for combining known reaction data to deduce the enthalpy change of an unknown reaction.

Transcript

00:01 All right, guys, we're going to be doing question number 66, x from chapter 5 in chemistry, the central science.

00:10 Thanks, we're going to be using these equations to figure out what the, us to isolate this equation and find out what the change in enthalpy is.

00:19 You can find, if you add two chemical equations together, you can find the overall change in enthalpy for those reactions together by adding together the delta h values.

00:34 So that's what we're going to be doing.

00:39 So we need to find equations with n -2 on the left.

00:43 And we see that here.

00:45 So we're going to use this equation first.

01:16 So we have delta h is equal to 180 .7 kilojoules.

01:30 Now, let's go through our other equations.

01:33 So here we have n2 on the right.

01:34 We have to move it to the left.

01:36 So it's here.

01:37 And we also have an n2 on the left.

01:38 We have to move that to the right.

02:26 So delta, delta, delta h is not going to be 113 .1 kilojoules.