If a sample of Au=0.129 J/g*C absorbs 255 J to increase the temperature from 18*C to 39*C what would the answer be in J ?

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?