Chemical Reaction

7A: Chemical Changes

• Chemical Reaction: a process that rearranges the atoms in one or more substances into one or more new substances

Evidence of Chemical Change

• Bubbles: a chemical reaction between two liquids may produce a gas. the gas is seen as tiny bubbles

• Precipitate: sometimes when two liquids are mixed together, a solid will separate from the mixture. the solid that forms is called a precipitate

• Energy Released: many chemical reactions release energy, which can be in any of many forms.

• Odor: some chemical reactions produce a distinctive smell

• Temperature Change: chemical reactions typically release or absorb energy. releasing or absorbing energy is often observed as a temperature change in the new substance being formed

• Color Change: the new substance formed by a chemical reaction may be a different color than the original substances

• Composition Change: all reactions experience a composition change, some more obvious than others.

• Burning: other chemical reactions produce a visible flame as they react

Writing Chemical Equations

• Chemical Equation: a combination of chemical formulas and symbols that models a chemical reaction

• Reactant: a substance that enters into a chemical reaction

• Product: a substance that is formed during a chemical reaction

Working With Chemical Equations

• Mole: SI fundamental unit for the quantity of matter in a substance; a count equal to 6.022 x 10^23

• Molar Mass: the mass of one mole of a substance

7B Types of Chemical Reactions

Reactions:

• Synthesis Rreaction: a chemical reaction in which two or more reactants combine into a single, more complex product

• Decomposition Reaction: a chemical reaction in which a single reactant breaks down into two or more products

• Single-Replacement Reaction: a chemical reaction in which one element in a compound is replaced by another element

• Double-Replacement: a chemical reaction in which two compounds swap cations or anions with each other

• Combustion: an exothermic chemical reaction in which a fuel reacts with oxygen

• Oxidation: a positive or negative number showing the electric charge on an element when it forms a compound '

• Reduction: a gain of electrons in a chemical reaction

7C Energy in Chemical Reactions

Energy Out - Energy In

• Exothermic Reaction: a chemical reaction that releases more thermal energy than it absorbs

• Endothermic Reaction: a chemical reaction that absorbs more thermal energy than it releases

• Activation Energy: the minimum energy needed for a chemical reaction to occur

• Law of Conservation of Energy: the law that states that matter can neither be created or destroyed but only transferred between objects

7D Reaction Rates and Equilibrium

Collision Model: the model that states that for a reaction to occur, the reactant particles must collide with each other, with the proper alignment, and with enough energy

reaction rate: the speed of a reaction

Factors That Affect Reaction Rates

• Surface Area: reactions happen only where the reactants are in direct contact If the surface area of the reactants is increased, then more reactant particles will be in contact with each other and more reactions will take place

• Stirring: stirring the reactants moves more reactants into contact with each other, causing more reactions to occur

• Temperature: increased temperature means the particles move faster, resulting in more reactions

• Concentration: as the concentration reactants - how many particles are in a certain volume - it is increased, more collisions occur, increasing the rate of reaction