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. 

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.

D=m/v m=d*vd=densitym=massv=volumed(ether)=0.71 gr/cm³=0.71 gr/ mlv=130 mlm=d*vm=0.71 gr/ml*(130 ml)=92.3 gm=92.3 g