If reactants a and b contain a total of 248 kj of chemical energy, and products c and d contain a total of 841 kj of chemical energy, is the reaction endothermic or exothermic?

The answer is endothermic.

Reaction is endothermic

Explanation:

The given reaction is :

A + B → C + D

The enthalpy change of a reaction (ΔH) is given by the difference between the enthalpy of the products and that of the reactants.

ΔH = H(products) - H(reactants) (1)

Now, enthalpy is a form of chemical energy which is essentially a measure of the heat content of the system. It is given that:

Chemical energy of reactants (A+B) = 248 kJ

Chemical energy of products (C+D) = 841 kJ

Based on equation (1) we have:

ΔH = H(C+D) - H(A+B) = 841-248 = +593 kJ

Since, the enthalpy change is positive, this implies that the reaction is endothermic i.e. energy is absorbed or required to carry out the reaction.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.

the answer is option a.