[Gxb217]

If energy is directly related to mass through E=MC^2, then how can an electron or particle gain energy without an increase in mass?

Does it has to do with the kinetic versus potential energy?

[ATMyller]

Mass is not the only form of energy. A particle can gain energy by other means than just mass increase.

[Borek]

If energy is directly related to mass through E=MC^2, then how can an electron or particle gain energy without an increase in mass?

Rest (or invariant) mass is constant. Relativistic mass is the one that gets larger when the particle gains speed. So yes, fast particles are heavier.

[Gxb217]

Borek,
Thank you very much. I was able to make the connection between this and kinetic energy in physics and that solved my questions

Gxb217

[Enthalpy]

Any form of energy gain results in a mass increase. Not only for particles.
But only concentrated forms of energy make a substantial variation that is perceivable or numerically usable: strong force, nuclear electrostatic repulsion, relativistic speed...

[lucerosoliz]

Mass–energy equivalence states that any object has a certain energy, even when it is stationary.