(in a random order, sorry)

— FROM PREVIOUS CHAPTERS

Factors that affect the rate of a reaction -

• The surface area of a solid reactants

• concentration of reactants

• pressure of reactants

• temperature

• presence of catalysts

Physical change - substance’s chemical properties remain the same. all processes are reversable. physical changes do not produce any new chemical substances.

Chemical change - substance’s chemical properties changes. most processes are irreversible. during chemical reactions, new chemical substances are formed and are very different from the reactants. some signs can let us know if a chemical reaction occured or not, they are:

• color change

• flame being formed

• precipitate being formed

• bubbles of gas being produced

• smell is detected

• change in temperature

+ temperature is needed for both physical and chemical changes to occur.

Examples of Physical and Chemical changes

Chemical - Combustion, Rotting, Rusting, Digestion

Physical - Melting, Shredding, Boiling, Chopping.

Rate of reaction - a messure of how fast or slow a reaction occurs. (physical / chemical)

Catalyst - a substance that increases the rate of a reaction by reducing its activation energy which increases the frequency of collisions between particles. (the catalyst remains uncharged).

Collision Theory - says that a chemical reaction happens only when the particles of the reactants collide with enough energy to start the reaction. the only way for a reaction to happen is when the particles collide with each other and their combined energy is higher than their activation energy.

Electrolyses - the process in which an electrical current flows through a liquid compound or solution. during this process the breakdown of an ionic compound happens due to electricity use.

Anode - positive electrode, attracts the negative.

Cathode - negative electrode, attracts the positive.

(colors of gases when they act in electrolyses, formed at anode)-

• Cl2 - green gas

• Br2 - brown gas

• F2 - pale yellow gas

Electrode - a rod made of Graphite and Platinum through which an electric current flows into or out of an electrolyte.

Electrolyte - the ionic molten compound or the aqueous solution that conducts the electricity.

Positive ions move towards the cathode where they gain electrons. And Negative ions move towards the anode where they lose electrons.

Electrons are the charge carries in the external circuit, and ions are the charge carries in the electrolyte.

Enthalpy - the amount of heat (thermal energy) contains in a system. the transfer of thermal energy during a reaction is called Enthalpy Change ΔH. ΔH is either a negative or positive value depending on wether the reaction is exothermic or endothermic.

Activation energy- minimum energy needed for a reaction to occur, particles need a certain amount of energy to start colliding with each other. the greater the intial curve in an Energy level diagram is, means the more energy is required for the reaction to begin.

Exothermic - process that releases heat, causes the surroundings temperature to increase. (occurs for making bonds)

Endothermic - process that absorbsheat, causes the surroundings temperature to decrease. (occurs for breaking bonds)

Exothermic / Endothermic diagram - is called Energy Level Diagram or Reaction Pathway Diagram.

Combustion - occurs in pressure of oxygen / when a substance reacts with oxygen, releasing heat, so it is also an exothermic reaction. during combustion, the substance involved is oxidised / gains oxygen !

Redox reactions

O2 - a lose of oxygen is called reduction. a gain of oxygen is called oxidation.

H2 - a lose of hydrogen is called oxidation. a gain of hydrogen is called reduction.

Ions - a lose of electron is called oxidation. a gain of electron is called reduction.

Mass = number of moles X molar mass

Number of moles = mass / molar mass

Molar gas volume = 1 mole of any gas, has a volume of 24dm(cube) at room temp.

Avogadro number = 6.02 × 10²³

"Describe a Balanced Equation.”

- An equation is balanced when the number of atoms for each element is the same for both reactants and products.

Hydrogen - Oxygen fuel cell

a hydrogen-oxygen fuel cell uses the reaction between hydrogen and oxygen to produce electrical energy. fuel, (hydrogen) donates electrons at one electrode and oxygen gains electrons at the other electrode.

the only chemical product made is water and there are not pollutants!

Advantages

• do not produce any pollution.

• have hgih efficiency

• no power is lost in transmission

• produce less noise pollution

Disadvantages

• manifacture of cells is expensive

• hydrogen is difficult to handle

• affacted by low temperatures, becomes less efficient

• only small number of of hydrogen filling stations across the country

• methods pollutants into the atmosphere

— FROM NEW CHAPTERS (7 and 8)

Acid and Bases

Properties of Acids

• pH level below 7

• sour in taste

• react with some metals to give hydrogen gas

• conduct electricity in solution

• contain hydrogen ions

• litmus paper + methyl orange = red color

Properties of Bases

• pH level above 7

• bitter in taste

• feels slippery

• dissolve fats and oils

• high concentration of OH

• litmus = blue color, methyl orange = yellow color

Bases - can neatralise an acid and give a salt and water only. but most bases dont dissolve in water. Bases are the oxides and hydroxides of metals!

Alkali - basess that also neatralise acids, but are also soluble in water! Alkalis are the hydroxides of metals.

Corrosive Acid - a highly reactive acid that causes damage to living tissues and other materials.

pH scale - a numerical scale which is used to show how acidic or basic a solution is. (from o to 14) Also called Sorensen Scale !

Indicator - substance that we use to put in solutions to check if the solution is acid or alkaline. the substance changes color depending on wether its an acid or base.

Different types of Indicators:

• Litmus (Paper)

• Methyl Orange

• Universal Indicator

- only metals above hydrogen in the reactivity series will react with dilute acids.

Acid + Base = Salt + Water

Acid + Metal = Salt + Hydrogen

Acid + Metal Carbonate = Salt + Carbon Dioxide + Water

Metal + Oxygen = Basic Oxide

Non-Metal + Oxygen = Acidic Oxide

—

Most common Acids - HCl, H2SO4, HNO3

Most common Bases - CaO, MgO

Most common Alkalis - NaOH, KOH, Ca(OH), NH3, NH4OH

—

• all acids have H+ ions

• all bases have O2- ions

• all alkalis have OH- ions

Amphoteric oxides - compounds that can act as base as well as acid in order to make salt and water.

- the concentration of hydrogen ions and hydroxide ions in water is equal.

- in a neatralisation reaction, H+ ions react with OH- ions to make water.

Periodic Table

Elements are arranged in order of increasing proton number.

Groups - all elements of the same group have the same chemical properties becuase they have the same electronic structure.

Periods - all elements of the same period have the same number of shells.

The Periodic Table is divided into 2 main groups, Metals and Non-Metals.

—

Group 1 - Alkali Metals the most reactive metals

• get more reactive as you go down the group

• hardness decreases as you go down

• density increases as you go down

• low melting and boiling points

• stored under oil to stop them from reacting

• conduct heat and electricity

Group 7 - Halogens the most reactive non-metals

• name of their ions (negative) is Halides

• get more reactive as you go up the group

• poisonous and have a strong smell

• are diatomic molecules

• boiling and melting point increases going down

• density increases going down (thats why they change from gas to liquid and to solid going down)

• color turns from pale to dark, as going down

Transition Metals useful metals

• metals with high densities and high boiling and melting points

• some are strogly magnetic (iron, cobalt, nickel)

• many form colored compounds

• have more than one valency

• some can act up as catalysts

• less reactive than other metals

• hard and strong, high density

• good conductors of electricity and heat

• malleable and ductile

• many have high resistance againts corrosion

Group 8 - Noble Gases non reactive gases

• have a full outer shell, so are stable

• exist as single atoms

—

Displacement reaction - reaction where the most reactive elements takes the place of the least reactive elements.

Melleable - can be hammared to shape without breaking.

ductile - can be stratched to wires without breaking.