# Why is an aldehyde more reactive than a ketone?

By definition, a ketone has a formula of $R C \left(= O\right) R '$, where $R$ is a hydrocarbyl group. On the other hand, an aldehyde has a general formula of $R C \left(= O\right) H$. The steric bulk of an hydrogen atom is very small compared to even a methyl group, and this is consistent with the enhanced reactivity of aldehydes versus ketones.