Let there be an object having some chemicals in it. It starts moving w

Let there be an object having some chemicals in it. It starts moving with a uniform velocity v and a chemical reaction starts happening. In this case, which of the following statement/s is/are correct ?

  • 1. Chemical reactions happening in the system cannot change the velocity v of the center of mass of the object.
  • 2. Chemical reactions happening in the system cannot change the kinetic energy of the particles inside with respect to the center of mass of object.

Select the correct answer using the code given below :

1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC NDA-2 – 2019
The correct option is A) 1 only. Statement 1 is correct, while statement 2 is incorrect.
Statement 1: The velocity of the center of mass of a system can only be changed by external forces acting on the system. Chemical reactions happening *within* the object involve internal forces between constituent particles. Internal forces cannot change the motion of the center of mass of the system. Therefore, if the object is moving with uniform velocity (implying zero net external force or balanced external forces), a chemical reaction inside will not change the velocity of the center of mass.
Statement 2: Chemical reactions often involve changes in the internal energy of the system, which can include changes in the kinetic energy of the particles relative to the center of mass (manifesting as temperature changes). For example, an exothermic reaction releases energy, which increases the kinetic energy of the constituent particles. Therefore, chemical reactions *can* change the kinetic energy of the particles inside with respect to the center of mass of the object.
The total momentum of the system remains constant in the absence of external forces, which means the velocity of the center of mass remains constant if mass is also constant. The total energy of the isolated system is conserved, but this energy can be converted between different forms, including internal potential energy (chemical energy) and internal kinetic energy (thermal energy, kinetic energy of particles relative to CM).