Chemical Reactions and Balancing Equations

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Defintions

Chemical Reaction may be represented using chemical equation. A chemical equation may be written in words or symbols. A symbolic equation is a set of chemical symbols and formulas that identify the reactants and products in words or symbols

Law of Conservation of mass

-Atoms are neither destroyed or produced in as chemical reaction.

-Total number of each kind of atom presenta t the start of the reaction equals the total number of each kind of atom after the reaction.

-total mass of all reactions involved in a chemical reaction is equal to total mass of all products

Chemical Change

- Conversion of pure substances (elements or compounds) into other pure substances with other properties. －　we can identify chemical change from color change, bubbling, production of gasses.

Chemical reactions

ONe or more chemical changes that occur at the same time; represented by chemical equations.

(a) Word equation: use the words to show a chemical reaction

eg. nitrogen monoxide + oxygen ---------> nitrogen dioxide

(b) skeletal equation: set of chemical symbols and formulas that identify the reactants and products in a chemical reaction eg. NO(g) + O2 (g)------------> NO (g)

(c) balanced equation: shows complete formula of reactants and products, follows law of conservation of mass eq: 2NO (g) + O2 (g) -------------> 2NO (g)

state of Compound

(g)= gas

(aq) dissolved in water

(s) - solid

(l)- liquid

method of balancing chemical equations

Balancing equation: shows complete formula of reactants and products, follows law of conservation of mass.

1. Write the symbols to represent reactants and products eg. H2 + O2 -----> H2O

2. Check each type of atom to see if there is an equal number of atoms on each side of the equation. If not add numbers (coefficients) in front of that element (or compound) to balance eg. H2 + O2 ----> 2H2O

3. Check to make sure the other atoms in the equation also balance.

eg. 2H2  +  O2   ------>  2H2O

4. If necessary, repeats steps 2 and 3 until everything balances. (this is a Trial and error process)

Four main factors that affect reaction Rate:

(1) Temperature: -increase temperature --> increase energy of particles--> particles move quickly and collide more with each other -high temperature --> faster reaction -lower temperature --> slower reaction

(2) Concentration -concentration = how much solute is dissolved in a solution (how much "stuff" in a given area) -more particles in less space --> less room to move --> more collisions between reactant particles -Lower concentration : less particles --> less chance of collision--> lower reaction rate

(3) Surface Area -surface area = measure of how much area of an object is exposed -many small particles will have more surface area than one large particle. -more surface contact --> high reaction rate -less surface contact --> lower reaction rate.

-surface area is NOT a factor if both reactants are gases or liquids (solid must be involved)

(4)Presence of catalyst catalyst= substance that speeds up the rate of a chemical reaction without being used up in the reaction itself. -reduce amount of energy required to break bonds between elements --> less energy required for reaction to occur --> faster reaction reaction rate Enzyme= catalyst present in a living cell, speed up metabolic reactions