Chemical Reactions
Chemical reactions are just the rearrangement of atoms
The new substances that are formed during a chemical reaction are called the products. The original substances are called the reactants.
The Law of Conservation of Mass
According to the Law of Conservation of Mass, the mass of what you start off equals the mass of what you end up with.
Balancing Equations
To balance equations, use times tables.
Acids and Bases
Acids are corrosive substances. That means they react with solid substances, ‘eating’ them away. Acids have a sour taste.
Bases, on the other hand, have a bitter taste and feel slippery or soapy to touch. Some bases are very corrosive, especially caustic soda (sodium hydroxide).
Acid Examples
Common Acids
Base Examples
Common Bases
Hydrochloric acid (HCl) in gastric juice.
Sulphuric acid (H2SO4)
Nitric acid (HNO3)
Carbonic acid in soft drink (H2CO3)
Uric acid in urine.
Ascorbic acid (Vitamin C) in fruit.
Citric acid in oranges and lemons.
Acetic acid in vinegar.
Sodium hydroxide (NaOH) or caustic soda.
Calcium hydroxide ( Ca(OH)2 ) or limewater.
Ammonium hydroxide (NH4OH) or ammonia water.
Magnesium hydroxide ( Mg(OH)2 ) or milk of magnesia.
Many bleaches, soaps, toothpastes and cleaning agents.
Alkalis
Alkalis a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0.
pH Scale
The pH scale ranges from 0 to 14. Low pH numbers (less than pH 7) mean that substances are acidic. High pH numbers (more than pH 7) mean that substances are basic (or then other word you will see is the term 'alkaline'). If a substance has a pH of 7, it is said to be neutral — neither acidic nor basic.
Exothermic and endothermic reactions
Endothermic Reactions
Endothermic and exothermic reactions involve the rearrangement of atoms, just like any other. Endothermic reactions ABSORB energy from the surroundings, and can often feel COLD to the touch. e.g. ice pack draws heat from your injured ankle.
Exothermic Reactions
Exothermic reactions are the opposite. They RELEASE energy in the form of HEAT, which can feel HOT to the touch. e.g. combustion.
Combustion Reactions
Combustion reactions are those in which a substance reacts with oxygen and heat is released. This makes it an exothermic reaction. Burning is a combustion reaction that produces a flame. The substance that reacts with oxygen in a combustion reaction is called a fuel.
Uses of Combustion
gas ovens, cars, and fossil fuel power plants. Combustion reactions are mostly used as a source for heat and light. Fire is a big use of combustion.
Acid Rain
Acid rain describes any form of precipitation with high levels of nitric and sulphuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth.
Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain falls because of human activities. The biggest culprit is the burning of fossil fuels by coal-burning power plants, factories, and automobiles.
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