My book states that Heat and work represent energy in transit. The state of the system undergoes a change after heat is supplied to it and before work is extracted from it because energy gets stored in it. My doubt is here that ,heat has been transferred to the system and it says heat is energy in transit and can't be stored but then it says system undergoes change cause energy is stored in it . This makes me confused. Please someone make me understand the concept behind this ,I know I have a big misconception .