How does heat transfer takes place between any two systems?

Explanation:

For transfer of heat between any two substances or matter can be occurred by conduction or convection process.

Conduction is a process in which two objects of different temperature are placed in contact with each other. Therefore, heat transfers from hotter object to colder object until the temperature of both objects becomes equal.

For example, a metal spoon placed in a hot cup of tea.

Convection is a process in which a fluid generally liquid or gas is heated and denser material (colder) sinks at the bottom whereas less denser material (hotter) rises at the top. This causes conventional currents in the fluid.

For example, heating rice in a pot full of water.

14,16 18 reacts with group

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.