Question

A mixture of gases A2 and B2 are introduced to a slender metal cylinder that has one end closed and the other fitted with a piston that makes a gas-tight seal so that the gases are a closed system. The cylinder is submerged in a large beaker of water whose temperature is 25 °C, and a spark is used to trigger a re-action in the cylinder. At the completion of the reaction, the piston has moved downward, and the temperature of the water bath has increased to 28 °C. If we define the system as the gases inside the cylinder, which of the following best describes the signs of q, w, and ∆E for this reaction?

(a) q60, w60, ∆E60

(b) q60, w70, ∆E60

(c) q60, w70, the sign of ∆E cannot be determined from the information given

(d) q70, w70, ∆E70

(e) q70, w60, the sign of ∆E cannot be determined from the information given

Answer 1

Here the cylinder containing gas is system and beaker used for water bath is surrounding .

For q

Since the temperature of surrounding is increased, this means surrounding is gainibg energy so system is loosing energy.

So q should be negative because heat is lost by system

For W:

Since the piston moves downward this means gases are compresses . Hence the work is done on the system. So,

W is positive.

For ∆E:

The change is internal energy is temperature dependent. If the temperature of the system is decreased then ∆E will also decrease .That is it will be negative .