A plumber is going to put two pipes in a wall, one in front and one in back. The pipes will be touching once they are installed. Both pipes are the same size and have the same number of molecules. The diagram above shows the pipes now, before they have touched. Use the information in the diagram to answer the question.

How does the temperature of the front pipe compare with the temperature of the back pipe before the pipes touch? What will happen after the pipes have been touching for a while?