Question

When hydrochloric acid and zinc were combined, the flask was sealed and thus no gas could escape from the flask. why did the pressure decrease as the temperature decreased?

Answer 1

When hydrochloric acid and zinc were combined, the salt zinc chloride and hydroge gas are being produced in the flask. The flask was said to be sealed and, therefore, no gas could escape from the flask. As the temperature decreases, the pressure inside would decrease since the gas would have lower kinetic energy and would have less force to exert on the walls of the flask. This is also evident from the equation PV = nRT. As we can see pressure and temperature are directly related which means as one decreases, the other decreases as well or as one increases, the other would increase accordingly.

Answer 2

Explanation:

According to the the ideal gas law, PV= nRT.

This means that pressure is directly proportional to temperature.

So, when HCl and zinc are combined in a flask then it will lead to the formation of zinc chloride and hydrogen gas.

The reaction equation will be as follows.

             $HCl + Zn \rightarrow ZnCl_{2} + H_{2}$

Since, the flask is sealed hence, hydrogen gas will not be able to move out of the flask.

So, when it will behave ideally then due to directly proportional relation between pressure and temperature there will occur a decrease in temperature with decrease in pressure.