Enthalpy of Formation Example 1

Jules Bruno
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here in this example question. It says the reaction of methane with chlorine gas is illustrated by the reaction below. Here. We need to calculate the entropy of reaction the standard entropy of reaction if the standard entropy ease off formation for methane, carbon tetrachloride and hydrochloric acid are negative. 74.87 1 negative 1 39 and negative. 92.31 killer jewels per mole, respectively. All right, so step zeros. We check to see if the chemical reaction is balanced and if not, then do the necessary steps to balance it here. We already have the equation balance. So that's great. That means we can move on to step one. Step one says starting with the products multiply the coefficients, sold the numbers and read off each substance with their entropy off formation value. Alright, So here we're going to say that we have one mole off carbon tetrachloride and four moles of HCL. We said here that carbon tetrachloride has a value associated with negative 39 kg promote and hydrochloric acid has negative 92.31 Here, the moles will cancel out and we'll have killer jewels left So this is negative. 9 to 5.24 killer jewels. Next we're going toe, go to the reactant. Also multiplied their coefficients off each substance with their rental piece of formation. Not realize here that for C l two I didn't give us an entropy formation because earlier we said that if an element is in its standard or natural state, it's entropy. Formation is equal to zero C l two. Gas is the natural form off chlorine. So it has an entropy of zero. Methane is negative, 74.87 we have one more. And here we have formals moles cancel out and what we left with killer jewels four times 00 So that doesn't matter. So this is just simply negative 74.87 killer jewels. Now that we have the amount for products and reactions, we go to step three. We take both totals and place them into the standard heat of reaction formula to determine the standard entropy of reaction. So products was negative. 9. 25.24 Killer jewels and reactions was negative. 74.87 Killer jewels Delta H Standard dealt on entropy of reaction equals products minus reactions. When we plug that in, that gives us negative 8 50.37 killer jewels as our answer. So yet this is another way that we're able to calculate the standard entropy of reaction. In this case, we did it through the use of the entire piece of formation for each of the substances within the chemical reaction.