Thermochemistry Concept Questions?

  1. List the 3 things to know about a catalyst.

  2. What happens in an endothermic reaction?

  3. What happens in an exothermic reaction?

  4. How is kinetic energy related to temperature? How is it related to particle motion?

2 Answers

look below.



  • Does not affect change in enthalpy (#DeltaH#).
  • Lowers #E_a# (both forward #E_a# and reverse #E_a#) (activation energy for a reaction to occur).
  • Speeds up a reaction. By decreasing #E_a#, it decreases the #E_a# "hill" and therefore the reaction is sped up.


  • Energy is gained by the system, and lost from the surroundings (the reaction/system absorbs energy from the surroundings)
    -the products have more energy than the reactants


  • Energy is lost from the system, and gained by the surroundings (the reaction/system releases energy and is absorbed by the surroundings)


  • As the temperature increases (the temp of reactants increase) the #K_(avg)# (average kinetic energy, and NOT just kinetic energy) increases, thus, increasing reaction rate.

It's directly proportional to particle speed (collision theory) because the particles must not only have the correct orientation at impact, but they also need sufficient activation energy at impact (#E_a#)

May 8, 2018

1.) They affect the speed of chemical reactions
2.) The reaction will appear cold
3.) The reaction will appear hot
4.) Hotter an item is the faster the particles move


For #1 I don't know exactly what you're looking for but catalysts typically speed up chemical reactions, making some that would take very long much easier to observe or study. In a chemical equation a catalyst would be expressed as such: enter image source here

#2, Endothermic means that the reaction absorbs surrounding heat, causing the reaction to feel cold. This can in part have to do with the electrons moving to higher energy levels, requiring more energy to make their jump.

#3 Exothermic is precisely the opposite, the reaction gives off heat energy, causing it to feel hot. Inversely, in an exothermic reaction the electrons would be moving to lower energy levels, expelling heat as they don't need as much energy to be at a lower energy level.

#4 Kinetic energy is directly related to temperature, meaning when one raises the other also does and vice versa. Also, the more thermal energy a particle has, the more entropic the particle will become.