Question

Question 5: Answer the following questions regarding heat or work. Explain your answer for full credit (4 points). A. A container has a certain amount of hydrogen. The container is compressed. Should work be positive or negative if we consider hydrogen our system? B. Dr. Burns' brother Nolan makes a snowball in his hand. Heat from his hand melts the snowball. Should "q" be positive or negative if the snowball is our system? C. Metallic zinc is dropped in a solution of hydrochloric acid and the container this reaction takes place in expands. Should work be positive or negative if the chemical reaction is our system? D. Gasoline is combusted in a car engine. Should "q" be positive or negative if the combustion reaction is our system?

Answer 1

A. when a container containing hydrogen gas is compressed where the hydrogen gas is system, the work is done on the system and therefore it is "positive". On compression, the energy is transferred to the gas and thus work is done on the system.

B. Here snowball is considered as system and heat from hand was transferred to snowball/system. Since heat is absorbed by system, q will have positive value.

C. When the chemical reaction is system, the work is done by the system in the form of undergoing a chemical process, therefore the work is negative.

D. Gasoline undergoes combustion (combustion is our system) and during this process the heat is produced by system or in other terms energy leaves the system. There fore "q" is negative.