Question

An exothermic reaction is conducted in an insulated calorimeter filled with water. The calorimeter is then sealed so that there is no heat exchanged between the contents of the container and the surrounding air. All of the following statements correctly describe what will happen over the course of the reaction except Your answer: A. the thermometer will show an increase in temperature. B. the potential energy of the products will be lower than that of the reactants. C. the total energy inside the calorimeter will decrease. D. the water increases in temperature as the reaction gives off heat.

Answer 1

Answer: option C. the total energy inside the calorimeter will decrease.


Justification:

The answer is a direct application of the first law of thermodynamic (the law of conservation of energy).

By telling that the the calorimeter is sealed so that there is no heat exchanged between the contents of the container and the surrounding air, the first law of thermodynamics implies that the total energy inside the calorimeter will not change.


That statement, without adding any more is enough justification.


Regarding, the other statements, you can show they are true:

A. the thermometer will show an increase in temperature.


Since the reaction is exothermic, the heat released will increase the temperature inside the sealed calorimeter,which, of course, is shown by the termometer.



B. The potential energy of the products will be lower than that of the reactants.


In any exothermic reaction, the potential energy of the products is lower than that of the reactants, because the heat released is lost by the reactants when they react and transform into the products.


D. The water increases in temperature as the reaction gives off heat.

Sure. The heat cannot leave the sealed calorimeter, but the water inside the calorimeter will absorb that heat: the molecules of water will gain kinetic energy and so its temperature will be increase.