Chinese grammar: 了2 (Modal Particle 了) - Youtube - Cchatty

了2: (Modal Particle, 语气助词）

了2 indicates a change;
1.1, A change that has occurred;
1.2, A change that is going to take place;

了2: 
2, 了2 used to express a tone;
2.1, It is used at the end of the declarative sentence to soften the tone;
2.2, It is used at the end of an exclamative sentence to enhance the tone.
 

the difference of 了1 (Aspect Particle, 动态助词) and 了2 (Modal particle, 语气助词): https://www.cchatty.com/grammar/10375