Chemical reactions and Enzymes

Bonds break and form during chemical reactions. Chemical reactions change substances into different substances by breaking and forming chemical bonds. Reactants are substances changed during a chemical reaction. Products are substances made by a chemical reaction. Chemical equations are used to show what happens in a reaction. Reactants are usually on the left side of the arrow, and products on the right. Bond energy is the amount of energy that will break a bond between two atoms. Different bonds have different required energies. When bonds are formed, energy is released. This energy is equal to the amount it takes to break that same bond. Many reactions are reversible and are denoted by arrows pointing in both directions. Equilibrium is reached when both reactants and products are made at the same rate.

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Check for Understanding! Explain why concentration is important in a chemical reaction. Concentration can alter the equilibrium of a chemical reaction. A higher concentration of reactants means that more of the reactants are available to react.

Chemical reactions release or absorb energy. Activation energy is the amount of energy that needs to be absorbed for a chemical reaction to start. Exothermic reactions release more energy than they absorb. Product energy is less than reactant energy Excess energy is given off as heat or light Ex. Cellular respiration releases energy for your cells and keeps our body warm Endothermic reactions absorb more energy than it releases. Products have a higher energy than reactants Energy is absorbed Ex. Photosynthesis, plants absorb energy and use it to make simple sugars and complex carbohydrates.

When enough energy is added to the reactants, bonds in the reactants break and the reaction begins. http://www.bbc.co.uk/staticarchive/410121c61d2de877dacf70be8eea8ea156a10425.gif

http://pyrodata.com/definitions/Endothermic-reaction

Check for Understanding! Is the amount of activation energy related to whether a reaction is exothermic or endothermic? Why? How is activation energy related to bond energy? No, the bond energies of reactants and products determine whether a reaction is exothermic or endothermic. The amount of activation energy required depends on the bond energy of the reactants.

A catalyst lowers activation energy. Activation energy is needed to get a reaction started. Once started, it can continue on it’s own, at a certain rate. Activation energy often comes from temperature increase. Catalysts are substances that decrease the activation energy needed to start chemical reactions and increase the rate of the reaction. Less energy needed Products form faster Not reactants or products because they aren’t changed or used up

http://www.chemguide.co.uk/physical/basicrates/catalyst.html

Check for Understanding! Describe two functions of catalysts in chemical reactions. Catalysts decrease activation energy and increase reaction rate.

Enzymes allow chemical reactions to occur under tightly controlled conditions. Enzymes are catalysts for chemical reactions in living things. Lower activation energy and increase reaction rate. Do not change reaction direction, only the time needed to reach equilibrium. Involved in almost every process in living organisms. Enzymes are proteins. Enzymes shape and function can be affected by temperature and pH.

Substrates are the specific reactants that bind to enzymes. Temporarily bind to enzymes at very specific active sites. If the structure of the enzyme changes, the substrate may no longer fit. Lock and key model Enzyme substrate complex Enzymes bring substrate close together Enzymes decrease activation energy Substrates bind to the active site and bonds are weakened, allowing for less activation energy to be needed http://i677.photobucket.com/albums/vv133/erica46829/LockandKeyTheory.jpg

Check for Understanding! How does the structure of an enzyme affect its function? If the structure of an enzyme changes, its function will change.