Question

measurements show that the enthalpy of a mixture of gaseous reactants increases by 278. kj during a certain chemical reaction, which is carried out at a constant pressure. furthermore, by carefully monitoring the volume change it is determined that 139. kj of work is done on the mixture during the reaction.
calculate the change in energy of the gas mixture during the reaction. round your answer to 3 significant digits. kj
is the reaction exothermic or endothermic?
exothermic
endothermic

Explanation:

Step1: Recall the first law formula

$\Delta U = q + w$ (at constant pressure, $q = \Delta H$)

Step2: Identify values

$\Delta H = +278\ \text{kJ}$ (enthalpy increases), $w = +139\ \text{kJ}$ (work done on system)

Step3: Calculate ΔU

$\Delta U = 278 + 139 = 417\ \text{kJ}$

Step4: Determine reaction type

Endothermic (enthalpy of system increases)

Answer:

417 kJ
endothermic