Dictionary Definition:

“The branch of chemistry or biochemistry concerned with measuring and studying the rates of reactions.”

Selected from OxfordDictionaries.com

Functional Definition:

Kinetic chemistry is reaction chemistry and it focuses on the rates at which reactions occur. Some things to consider when thinking about the rate of reaction are the properties and environment in which the reaction occurs.

• Think about what kind of reactants you’re working with. Are they ionic, covalent, or rely on another interaction? Are they polar or nonpolar? These characteristics are important because they can slow a reaction down. Large molecules are slow to react and covalent bonds are slow to form.
• You may also want to consider the physical states of the reactants. Whether they are gaseous, solid, or liquid may also determine how fast they will react and how easily they can form or break bonds. Solids may have low surface area and take longer to react, where as liquids may take less time.
• What is the temperature of your reaction? Increasing heat typically increases the rate of reaction where colder temperatures will tend to slow a reaction. The temperature of a reaction may also tell you what physical state the reactants are under. Knowing the temperature threshold for state changes is a huge part of understanding the effects of temperature on your reaction.
• How concentrated are your reactants? A higher concentration typically has a higher rate of reaction because there are more  molecular collisions.
• Is your reaction under standard pressure? increases in pressure increase molecular collisions in gaseous reactions, can effect state changes, and can condense reactants there by increasing concentration. Decreasing pressure will decrease reaction rates by spreading out gaseous reactants and effectively lowering the temperature of the reaction.
• Is there a catalyst? Catalysts are molecules/compounds that alter the rate of reaction but are not changed in the process of the reaction. The common explanation for a catalyst is a wooden spoon that mixes lemonade, breaking down the sugar that you’ve added and helping it dissolve. Catalysts are often chemical substrates in which a reacting molecule is made more susceptible to reaction. Examples include iron and platinum. Modern cars use catalytic converters to quickly convert toxic car emissions into smaller molecules via redox-reactions.  Catalysts are vital to biological reactions, without catalysts known as enzymes many processes would never occur or would occur at such a slow rate that they would never keep anything alive.