Consider the two space shuttle fuel reactions in Exercises 81 and 82. Which reaction produces mo

Consider the two space shuttle fuel reactions in Exercises...

Key Concepts

Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. In the context of the problem, it determines the exact proportions in which the reactants must combine (stoichiometric amounts) to ensure complete reaction without any excess reactant, providing a basis for comparing energy outputs from different reactions.

Enthalpy of Reaction

The enthalpy of reaction, often expressed as the heat released or absorbed during a chemical reaction, is a critical concept in comparing energy outputs. It quantifies the total energy change per mole of reactants under standard conditions, allowing one to analyze which reaction is more exothermic.

Energy Density

Energy density is the measure of energy released per unit mass of the reactant mixture. It is important in applications such as fuel reactions because it directly indicates how much energy can be obtained from a given mass of reactants, crucial for determining overall efficiency in propulsion and energy applications.

Molar Mass and Mass-Energy Conversion

This concept involves converting the energy change per mole (obtained through enthalpy calculations) into energy per unit mass by using the molar masses of the reactants. This conversion is essential to assess how much energy is produced per kilogram of the reactant mixture, facilitating direct comparisons between reactions.

Transcript

00:04 Let's consider the two space shuttle fuel reactions and exercises 81 and 82, which one produces more energy per kilogram of reactant mixture.

00:12 So from exercise 81, our reaction is 3 aluminum solid plus 3nh4 clo4 solid produces aluminum oxide solid, aluminum chloride solid, 3n0 gas, and 6 h2o gas.

00:56 So what we have to find here is we have to find the delta h0 reaction for this.

01:07 So the delta h .0 reaction is equal to the enthalpy formation for the products minus the enthalpy of formation for the reactants.

01:29 Let's define these expressions here.

01:31 We'll get a fairly large expression here.

01:33 This is equal to for the products.

01:37 3, delta h, not f, aluminum.

01:47 Of products, sorry.

01:49 I'm just trying to the reactants over the product.

01:51 So this is delta h.

01:54 Not f of a, l2 ,0.

01:58 Solid plus delta h not f a lcl3 plus 3 delta h not f of n o gas plus 6 delta h not f of h2 o gas minus dd not f of aluminum solid plus delta h not formation and h4 c l .4 solid so this would be equal to so you have to be formation for aluminum oxide it's negative 1 ,676 kilojoules plus for aluminum chloride negative 704 kilojoules nitrogen monoxide, 90 kilojoules, three times that for stoichiometry, and h2l gas is negative 242 kilojoules, must be minus, enthalpy formation for aluminum is zero, plus, enthalpy formation for ammonium per chlorate is negative 295, and suri.

03:57 I missed some threes here.

03:59 There needs to be a three here and a three here, three, and negative 295 kilojoules.

04:11 And solving for the enthalpya formation, we'll get negative 2 ,67 kilojoules.

04:20 So that would be the enthalpya formation from the reaction given in exercise 81.

04:27 So if we look at the reactants, our reactants are al and nh4 clo4.

04:51 So if we look at the for aluminum, we have three moles of aluminum, which will have a mass equal to 80 .94 grams.

05:07 And we have three moles of nh4c -l -o -4.

05:16 This will have a mass that is equal to 352 .4756 grams.

05:27 So the mass of the reactant mixture will be equal to 80 .94 grams plus 352.

05:45 And 6 grams and we'll find that this is equal to 433 .42 grams or in terms of kilograms 0 .43342 kilograms so therefore the amounts of energy released per kilogram would be equal to negative 2 ,677 kilojoules divided by 0 .3342 kilograms and we'll find that this is equal to negative 6 ,172 kilojoules per kilogram.

06:43 Now this would be from the reaction given in exercise 81...

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