Ethanol (C2 H6 O) reacts in the body using the following...

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\right)$ reacts in the body using the following equation: $(9.3,9.5)$ $\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}(a q)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+3 \mathrm{H}_{2} \mathrm{O}(l)+327 \mathrm{kcal}$ Ethanol a. Is the reaction exothermic or endothermic? b. How much heat, in kilocalories, is produced when $5.00 \mathrm{~g}$ of ethanol reacts with $\mathrm{O}_{2}$ gas? c. How many grams of ethanol react if $1250 \mathrm{~kJ}$ are produced?

Ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\right)$ reacts in the body using the following equation: $(9.3,9.5)$
$\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}(a q)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CO}_{2}(g)+3 \mathrm{H}_{2} \mathrm{O}(l)+327 \mathrm{kcal}$ Ethanol
a. Is the reaction exothermic or endothermic?
b. How much heat, in kilocalories, is produced when $5.00 \mathrm{~g}$ of ethanol reacts with $\mathrm{O}_{2}$ gas?
c. How many grams of ethanol react if $1250 \mathrm{~kJ}$ are produced?

Key Concepts

Exothermic and Endothermic Reactions

This concept distinguishes reactions that release heat (exothermic) from those that absorb heat (endothermic). Understanding the sign of the enthalpy change is crucial in thermochemistry because it indicates whether energy is expelled or consumed during the reaction.

Chemical Equation Stoichiometry

This concept involves using the balanced chemical equation to determine the quantitative relationships between reactants and products. It is fundamental for calculating how much of each substance reacts or is produced based on mole ratios.

Molar Mass and Unit Conversions

Molar mass is used to convert between a substance’s mass and the number of moles, which is essential in stoichiometric calculations. Additionally, converting energy units, such as between kilocalories and kilojoules, is necessary for accurately relating energy changes to the quantities of reactants used.

Enthalpy Change Calculations

This concept encompasses determining the total energy change of a reaction by applying the enthalpy change per mole from the chemical equation to the actual amount of substance reacting. This calculation is central to understanding how much energy is released or absorbed in a chemical process.

Transcript

00:01 Part a of this question is asking if the reaction is endothermic or exothermic.

00:05 Well, we see that on the right hand side, on the product side, we have a plus 327 kilocalves.

00:18 So this is indicating that although it says a plus, right, this is on the product side.

00:24 This is a product.

00:27 So therefore, this is actually going to be exothermic.

00:35 All right, that was part a.

00:39 Part b.

00:41 How much heat and kilocalories is produced when we take five, grams of ethanol and react it through this reaction.

00:48 Well, one mole of ethanol produces 327 kilocals.

00:54 So how many moles are in five grams? so we take five grams, and we're going to multiply it by our conversion factor, which is going to be the molar weight of ethanol.

01:08 So c2, h60.

01:11 So we know that carbon is a molecular weight of 12, and there's two of them, so that's 24, plus.

01:17 Six hydrogens which are each one unit so that gives us a total of 30 and then we add in the 16 which is the molecular weight of oxygen and that gives us 46 so 46 grams of ethanol is equal to one mole of ethanol and then we can go in and we can say oh five grams divided by 46 is 0 .11 moles so therefore if we put 0 .11 moles into this reaction, how many kilocalories do we get? well, we simply take our moles and multiply it by the product kilocalories, 327 kilocals per mole.

02:08 And as you can see, actually if we were to write it out like this, right, you see that the moles cancel, and you're left with your answer, which is in kilocalories.

02:19 So 0 .11 times 327, and we get 307.

02:32 That's the answer to part b.

02:34 Then finally part c, how many grams of ethanol react if 1250 kilojoules are produced? well, here the thing is, this is in kilojoules, and our initial reaction was given us a heat value in kilocalves...

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