Chapter+3+Chemical+Reactions

=__Definitions__ = **__Activity series:__** a list of elements arranged in order of their reactivity, based on empirical evidence gathered from single displacement reactions __**Alloy: **__ a homogenous mixture (a solution) of two or more metals **__Kinetic Molecular Theory:__** states that all matter is made up of particles in continuous random motion, temperature is a measure of average speed of the particles. __**Collision-reaction theory:**__ states that a chemical reaction reactions involve collisions and rearrangements of atoms or group of atoms, and the outcome depends on the energy and orientation of the collisions. **__Single displacement reaction:__** the reaction of an element with a compound to produce a new element and a new compound
 * __Chemical change:__** any change in which a new substance is formed
 * __Corrosion:__** the unwanted reaction of metals with chemicals in the environment
 * __Galvanizing:__** the coating of iron or steel with zinc to prevent rusting

= = = = = = = = = = =__Recognizing and Understanding Chemical Changes __=

A chemical change that releases large volumes of gases and a considerable amount of heat. Basically, any change in which a new substance is formed.

__**Table 1: Evidence of Chemical Reactions **__
 * < **Evidence** ||< **Description** ||
 * < Change in colour ||< Products have different colour that the colours of the reactants ||
 * < Change in odour ||< Materials that have a different odour than the odours of the beginning materials ||
 * < Formation of solid/ gas ||< Materials may include a substance in a state that differs from the starting one into a gas or a solid (precipitate) ||
 * < Release/ absorption of heat ||< Energy such as light, electricity, sound mostly heat is absorbed in an **//endothermic//** reaction and released in an **//exothermic//** reaction. ||


 * __Kinetic Molecular Theory: __**
 * 1) Matter is made up of small particles.
 * 2) They are in constant motion.
 * 3) The collide with each other constantly.
 * 4) The collisions depend on temperature and concentration.
 * 5) Collisions can lead to formation of products.

__**Factors Affecting Rates of Reaction:**__
 * Temperature
 * Concentration
 * Surface Area
 * Catalyst

__Temperature__ Rise in temperature the molecules and atoms move faster therefore the chance of them colliding with each other is higher. __Concentration__ Higher the concentration higher the molecules colliding and can change into products. __Surface Area__ Greater the area greater is the number of molecules exposed. Reactants interacting is higher and also increase rate of reaction. __Catalyst__ is a substance that changes the rate of a reaction without itself undergoing any change. Positive catalyst increases the reaction and negative decreases the reaction.


 * __

Single Displacement __** A+BC -> AC+B Element + Compound -> New Element + New Compound Examples: Mg (s) + CuSO4 (aq) -> Cu (s) + MgSO4 (aq) Magnesium is more reactive than copper displaces Cu from CuSO4 as Cu(s)

Cu (s) + AgNO3 (aq) -> Ag + Cu(NO3)2 Brown + Clear Colourless Transparent

Cu-> Cu 2+ + 2e 2Ag+ + 2e- ->2Ag Cu + 2Ag+ (aq) -> Cu2+ (aq) + 2Ag (s) Copper-> Blue

ZnSO4+ Cu -> This reaction will not take place. Cu is less reative. It cannot displace Zn From Zn SO4 or Zn is more reactive

__Most Reactive__ lithium potassium barium calcium sodium magnesium aluminum zinc iron nickel tin lead (hydrogen) copper silver gold __Least Reactive__

= Double Displacement Reaction =

This reaction occurs when elements from different compounds exchange places.

compound + compound  à compound + compound AB + CD  à  AD + BC

Sodium sulphate + Lead Nitrate  à Lead sulphate + Sodium nitrate Na2SO4 + Pb(NO3)2 <span style="FONT-FAMILY: Wingdings; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Wingdings"> à PbSO4 + 2NaNO3 =Prediction of Precipitation=

Precipitation reactions are processes in which soluble reactants yields an insoluble solid product that falls out of the solution, thereby removing some of the dissolved ions. Most precipitations take place when the anions and cations of two ionic compounds change partners. For example, an aqueous solution of lead(11) nitrate reacts with an aqueous solution of potassium iodide to yield an aqueous solution of potassium nitrate plus an insoluble yellow precipitate of lead iodide: Pb(NO3)2 aq + 2KI aq <span style="FONT-FAMILY: Wingdings; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Wingdings"> à 2KNO3 aq +PbI2 aq

=Neutralization Reaction=

Acid-base neutralization reactions are processes in which an acid reacts with a base to yield water plus an ionic compound called salt. We defined acids as a compound that produce H+ ions which dissolved in water and bases are compounds that produce OH- ions when dissolve in water. Thus, a neutralization reaction removes H+ and OH- ions from solution, just as a precipitation reaction removes metal and non-metal ions. The reaction between hydrochloric acid and aqueous sodium hydroxide to yield water plus aqueous sodium chloride is typical: HCl(aq) + NaOH(aq) <span style="FONT-FAMILY: Wingdings; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Wingdings"> à H2O(l) + NaCl(aq)