Gaseous ethanol, C2 H5 OH, is burned with pure oxygen in a constant-volume combustion bomb. The

step 1 And this problem, we have gaseous ethanol, which is C2H50H. It's burned with pure oxygen and a s

Gaseous ethanol, C2 H5 OH, is burned with pure oxygen in a...

Key Concepts

Thermochemical Data

Thermochemical data, such as the heats of formation and specific heats of the reactants and products, are essential for accurately determining the energy changes involved in a combustion reaction. These data allow for the quantification of the enthalpy change and, together with the principles of energy conservation, enable the determination of final temperatures in combustion processes.

Energy Conservation in Combustion

Energy conservation is a fundamental principle in combustion analysis. In an adiabatic system undergoing a constant volume process, the decrease in the reactants' internal energy, due to the chemical reaction, is entirely converted into an increase in the product’s internal energy. This conservation of energy is the basis for calculating the adiabatic flame temperature, where the chemical energy release directly translates into a temperature rise.

Adiabatic Flame Temperature

This concept refers to the maximum temperature achieved by a combustion process when no heat is lost to the surroundings. It is calculated based on the assumption that all the chemical energy released from the reactants is converted into thermal energy, making it a critical parameter in understanding and predicting combustion performance under idealized, insulated conditions.

Constant Volume Process

A constant volume process is one in which the reacting system does not change its volume during the reaction. In a combustion bomb, this means that the energy released from the chemical reaction results solely in an increase in pressure and temperature, with no work being done by the expansion of gases. This condition significantly influences the thermodynamic behavior and the calculations for the final state of the system.

Stoichiometric Mixture

A stoichiometric mixture is one in which the fuel and oxidizer are present in exactly the proportions required for complete combustion, meaning that there are neither excess reactants nor unburned fuel. This ratio is essential for maximizing combustion efficiency and for accurate energy balance calculations, as it ensures complete conversion of reactants into products.

Transcript

00:01 And this problem, we have gaseous ethanol, which is c2h50h.

00:07 It's burned with pure oxygen and a stoichiometric ratio, so we need three oxygen molecules, and we get two co2s and three waters out.

00:19 It's all in a constant volume combustion bomb.

00:24 So we have the, let's see, and we're assuming it's adeptic, and we want to find the final temperature, what they tell us? is greater than 5 ,000 kelvin.

00:39 So, we know in this case, because we have a constant volume, it's everything's enclosed.

00:45 It's the internal energy that is conserved from before, from the reactants to the products.

00:54 So for the reactants, the internal energy is the enthalpy of formation plus the change in enthalpy, up for being above the reference, minus the number of moles of reactants times the idios gas constant.

01:09 This is the number of gaseous moles of reactants times the adiogast constant times the pressure of the react, or the temperature of the reactants.

01:18 And likewise for the products.

01:22 So the entropy of formation for the fuel here is minus 235 megajoules per kilomole.

01:34 So what we can do here is we can, rearrange some things and i'm going to call this script h this value here which is basically the the change in internal energy above the reference well not really above the reference but this is the change in internal energy it's because it's the change in enthalpy and then changing it to converting it to the internal energy so we have let's see here that if we saw for the that here we get the this is be the entropy of combustion and then minus the the conversion with the for pv which we've used the ideal gas logic and our r bar t r now the entropy of formation we have the entropy of formation of the ethanol the enthalpya formation of the co2, the enthalpyal formation of the h2o, and then minus we have, let's see, this is the, for the reactants, this was gaseous, so we have four moles of, kilomoles of gas, and the ideal gas constant times the temperature of the reactants...

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