Final answer:
The energy for chemical reactions typically comes from heat energy in non-living systems and from ATP in biological systems. Heat energy improves molecular collisions, facilitating reactions, while ATP supplies energy for cellular reactions.
Step-by-step explanation:
The energy for practically every chemical reaction comes from various sources, depending on the context. In chemical reactions taking place outside of living organisms, such as the burning of gasoline in a car engine or coal to generate electricity, the primary source of energy is often heat energy from the surroundings. This heat energy increases the motion of molecules, which raises the frequency and force of collisions, allowing reactants to reach the transition state needed for reactions to proceed.
In biological systems, particularly within cells, energy comes from a high-energy molecule known as adenosine triphosphate (ATP). ATP, often referred to as the primary energy currency of cells, provides the necessary activation energy for endergonic reactions, which require the input of energy because their products have more free energy than their reactants. Overall, from daily energy usage to intricate cellular processes, the study of energy is integral to chemistry.