David’s mom wants to calculate how much it will cost to drive from los angeles, ca, to san francisco, ca. gas costs $4.00 a gallon, and the gas mileage of their car is 38 miles/gallon. what additional information does david’s mom need to do this calculation?

The distance between the two cities

While we know the cost of the gallons and the amount of miles per gallon, we do not know how far away each city is from each other.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.