A Level Chemistry OCR Practice Exam

What type of process is involved in the first ionisation energy?

1. A chemical reaction producing new substances

2. A physical process involving phase changes

3. A process that requires energy input to remove electrons

4. A reaction that releases energy

The correct answer is: A process that requires energy input to remove electrons

The first ionisation energy refers to the amount of energy required to remove one mole of electrons from one mole of gaseous atoms to form positively charged ions. This process involves overcoming the electrostatic attraction between the negatively charged electron and the positively charged nucleus of the atom. Since energy must be supplied to detach the electron from the atom against this attraction, it is an endothermic process, which inherently requires energy input. The context of other options clarifies their distinction. A chemical reaction would involve the creation of new substances through breaking and forming of bonds, which does not occur in the ionisation process. A physical process involving phase changes pertains to transformations of states of matter, like solid to liquid or liquid to gas, rather than the removal of electrons. A reaction that releases energy suggests an exothermic process, which contradicts the nature of ionisation where energy is needed to pull an electron away from an atom. Therefore, the correct understanding is that the first ionisation energy necessitates energy input to allow for the removal of an electron.