Which of the following most likely happens during a physical change? an irreversible process takes place. substance changes its form but not its molecular composition. new atoms are introduced in the molecules of the substance. a substance reacts differently with a chemical before and after the change. given two temperatures, 39 °f and 51 °f, which of the following correctly compares the number of chances for particles to bounce off each other during a chemical reaction? same at both lower at 39 °f lower at 51 °f does not depend on temperature

For the first one, the correct answer would be "Substance changes its form but not its molecular composition.". During a physical change (let's say cutting paper), the substance has its shape changed, but it is still itself (paper). 

The second one is a bit trickier: 
Kinetic energy of a molecule is directly influenced by temperature. If there is a higher temperature it will have a higher kinetic energy which means the molecule moves at a higher velocity. This will increase the chance of particles bouncing off of each other during the chemical reaction. That explains why the rate of reaction will be higher at a higher temperature, rather than higher at a cool temperature. The correct answer would be lower at 39F. 

Answer form flower;