Measurements show that the enthalpy of a mixture of gaseous reactants increases by 215. 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 -155. 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 2 significant digits. Is the reaction exothermic or endothermic?

The change in energy of the gas mixture during the reaction is 60 kJ. The reaction is endothermic.

Explanation:

According to first law of thermodynamics:

=Change in internal energy

q = heat absorbed or released

w = work done or by the system

w = work done on the system

w = -155 kJ

q = +215kJ   {Heat absorbed by the system is positive}

As the heat is absorbed and enthalpy increases, the reaction is endothermic.

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3