The enthalpy of combustion of solid carbon to form carbon...

The enthalpy of combustion of solid carbon to form carbon dioxide is $-393.7 \mathrm{~kJ} / \mathrm{mol}$ carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is $-283.3 \mathrm{~kJ} / \mathrm{mol}$ CO. Use these data to calculate $\Delta H$ for the reaction $$ 2 \mathrm{C}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}(g) $$

The enthalpy of combustion of solid carbon to form carbon dioxide is $-393.7 \mathrm{~kJ} / \mathrm{mol}$ carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is $-283.3 \mathrm{~kJ} / \mathrm{mol}$ CO. Use these data to calculate $\Delta H$ for the reaction
$$
2 \mathrm{C}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}(g)
$$

Key Concepts

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is independent of the pathway taken from reactants to products. This principle allows one to calculate the enthalpy change of a reaction by combining other reactions with known enthalpy changes, typically by reversing, adding, or multiplying these reactions to obtain the desired overall reaction.

Enthalpy of Combustion

The enthalpy of combustion is the energy released as heat when one mole of a substance completely reacts with oxygen to produce combustion products, typically carbon dioxide and water in the case of organic compounds. This value is useful in determining energy changes in processes involving burning or oxidation.

Reaction Enthalpy Calculation using Combustion Data

Calculating the enthalpy change for a reaction using combustion data involves setting up a Hess's Law cycle where the known enthalpies of combustion of the substances are used as building blocks. By appropriately manipulating these known reactions, one can derive the enthalpy change for the overall reaction of interest.

Standard Enthalpy Changes

Standard enthalpy changes refer to the heat change associated with a reaction under standard conditions (typically 298 K and 1 atm). These values provide a common reference point, allowing comparisons and the use of tabulated combustion and formation data in thermodynamic calculations.

Transcript

00:01 All right.

00:01 So for this problem, we have the enthalpy of combustion of solid carbon to form carbon dioxide, and it gives us the enthalpy, as well as the formation, the combustion of carbon monoxide to form carbon dioxide.

00:16 And we want to use that data to calculate delta a for this total reaction.

00:21 So it gives you these two reactions along with their anthopies, and it tells you what you want your desired reaction to end up being.

00:29 In order to determine the enthalpy of this final reaction, we have to manipulate these two up top in order to get there.

00:37 And whatever we do to the equations, we also do to the delta h.

00:42 So first thing i notice is carbon in our desired has two solid carbons, whereas my step here only has one.

00:51 So we're going to have to multiply everything by two.

00:57 And that includes your delta h.

00:59 So we're going to now have two, carbon solids plus two oxygen gases making two carbon dioxide gases and our new delta h is times two so we need to negative 390 3 .93 times two gives us negative 787 .4 now we need to take a look at this second one so so the first thing i notice about the second one is we want carbon monoxide gas as a product.

01:44 Here we have carbon monoxide gas as a reactant.

01:48 And there's only one in the step, whereas we want two in the final.

01:52 So we need to flip it and times two...

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