MCAT Chemistry > Chemical Reactions
Molecules are combinations of elements, which are held by strong chemical bonds. Bonds are formed via valence electron interactions. The resulting physical and chemical properties are completely different from constituent parts.
Na2+ (explodes in H20) + 2Cl- (toxic gas) combine to form NaCl (inert table salt)
Reactants are materials going into a reaction
Products are the materials coming out of the reaction.
Metabolism is when all of the reaction are occurring at one time within the body.
Decomposition reaction, also known as catabolism is when chemical bonds are broken down.
AB = A + B
One example of this is hydrolysis which breaks down water into different parts.
ABCDE + H2O = ABC-H + HO-DE
A synthesis reaction (anabolism) forms chemical bonds
A + B = AB
An example of this is dehydration where water is reconstructed from its constituent parts.
ABC-H + HO-DE = ABCDE + H2O
A reversible reaction is a chemical reaction that can occur in both directions at the same time. This is a reaction that may occur at equilibrium where the amounts of the chemicals do not change bot the reactions are still occurring. In fact, reversible reactions will seek to maintain a state of equilibrium if possible by creating balancing and opposing reaction rates. If reactants are added or removed it will cause the equilibrium point to shift to the most stable concentration.
AB - A + B
Chemical reactions in cells cannot occur with the presence of a catalyst or in biological functions, enzymes. The activation energy is the amount of energy required to initiate a reaction. Enzymes are the protein catalysts that are used to help lower the activation energy to start a specific reaction.
The process of enzyme activation greatly involves chemistry and biochemistry in order to function. Without enzymes the normal functions of the human body would occur on a scale that is not conducive to life and the maintenance of homeostasis.
See Atomic Structure
Atoms generally bond via the octet rule These tend to be the biological molecules such as:.
There are a few exceptions which include:
- All period 3 and below (more subshells)
See Ionic Bonds
See Covalent Bonds
See VSEPR Theory
Atomic and Molecular Orbitals are very important as the strength of intermolecular bonding impacts many physical properties such as melting/boiling points
Sigma (σ) Bonds are singular linear bonding orbitals that allow for free rotation and form when atoms bond head to head
Pi (π) Bonds are formed when two bonding orbitals are arranged parallel which restricts movement and does not allow free rotation.
- Bonding orbitals develop when overlapping orbital signs (+/-) are identical
- Non-bonding orbitals develop when the overlapping orbital signs are opposite
- Double Bonds are composed of 1 sigma and 1 pi bond
- Triple Bonds are composed of 1 sigma and 2 pi bonds
Click here to move onto stoichiometry.