Chemical ReactionsBy Aimee Chavez

Chemical EquationsTells the substances present before and after

the reaction.Reactants: what you start withProducts: what you end with

Conservation of MassIn a chemical reaction the mass of the

products always equals the mass of the reactants.

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.

Balancing EquationsIn order to show that mass is conserved

during a reaction, a chemical equation must be balanced.

Coefficients are numbers that appear before the formulas can be changed to balance an equation. Subscripts appear below and after an element or compound.

TipsIf a molecule or compound has a coefficient

and a subscript you multiply them together to find the total number of elements.

For example 2H₂O = H:4 and O:2

Step One1. Count the number of atoms of each

element on each side of the equation. Be careful to count correctly with coefficient

in front of a compound or molecules. For example the 2 in front of 2NaOH means Na:2 O : 2 and H : 2

Step Two2. Change one or more coefficients until the

equation is balanced. You always use the lowest possible

coefficient.Start on the right or left and keep going until

it is balanced.

Examples1. _____ H2 + _____ O2

_____ H2O

2. _____ N2 +_____ H2 _____ NH3

3. _____ S8 + _____ O2 _____ SO3

4. _____ N2 + _____ O2 _____ N2O

Classifying ReactionsTypes:

Type of Reaction

Definition Equation

Synthesis

Decomposition

Single Replacement

Double Replacement

A = Red B = Blue C = Green D = Yellow

A + B → AB

AB → A + B

AB + C → AC + B

AB + CD → AC + BD

Two or more elements or compounds combine to make a more complex

substance

Compounds break down into simpler substances

Occurs when one element replaces another one in a

compound

Occurs when different atoms in two different

compounds trade places

Identifying Chemical Reactions

____ P + O2 → P4O10 ____ Mg + O2 → MgO

____ HgO → Hg + O2 ____ Al2O3 → Al + O2

____ Cl2 + NaBr → NaCl + Br2 ____ H2 + N2 → NH3

2. Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type of reaction it illustrates. Use the code below to classify each reaction.

S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement

 

____ Na + Br2 → NaBr ____ CuCl2 + H2S → CuS + HCl 

____ HgO + Cl2 → HgCl + O2 ____ C + H2 → CH4

 

____ KClO3  →   KCl  +  O2  ____ S8 + F2 → SF6

 

____ BaCl2   +   Na2 SO4 →     NaCl   +   BaSO4

Speeding up Chemical Reactions1. Breaking a solid into smaller sizes (to

increase its surface area) 2. Increase the concentration (↑ substance)3. Increase the temperature ( more kinetic energy)

4. Decreasing volume5. Adding a catalyst

CatalystsA substance that modifies and increases the

rate of a reaction without being consumed in the process.

EnzymesImage result for

enzymeswww.chem4kids.comEnzymes are biological molecules (proteins)

that act as catalysts and help complex reactions occur everywhere in life. Let's say you ate a piece of meat. Proteases would go to work and help break down the peptide bonds between the amino acids.

Inhibitors

a substance that decreases the rate of or stops completely a chemical reaction.

Some reactions put out lots of heat. Extra heat may cause safety hazards - the engine may catch fire - or increase the likelihood of unwanted side reactions. (Watch out for that tree…)

Inhibitors also prevent chemical damage or decay in finished products. An anti-rust coating on your car is a good example of this.

Used in food production .

Chemical Changes1.Odor or Change in taste: (sour), Curdling of milk ,

browning fruit 2. Change in Color : Rusting/tarnishing, hair dye or bleach,

toast, burning toast or food3. Production of gas:(expanding /rising & bubbles), Baking a

cake or bread, Making cheese4. Hissing or Loud Noise (fire works)5. Formation of precipitate6. Protein rearrangement: frying and egg, eggs in baking a

cake7.Change in temperature: violent reaction (Fireworks)

that has heat as a product ( endothermic / exothermic)

Endothermic vs. Exothermic