C11 | 화학적 변화 (Chemical Changes) Flashcards
Chemical Changes
What are the two types of changes?
- Chemical Change
- Physical Change
What is the definition of a Physical Change?
A change in which no new substance is formed.
What is the definition of Chemical Change?
A change in which a new substance is formed.
How easy is it to reverse the process of Physical Changes?
Easy, we can get the substituents back using separation techniques.
How easy is it to reverse the process of Chemical Changes?
Difficult, we cannot get back the reactants easily.
What are some examples of Physical Changes?
- Change of State
(Boiling of Water) - Expansion & Contraction
What are some examples of Chemical Changes?
- Rusting
- Burning
What are the four types of Chemical Changes?
- Combustion
- Thermal Decomposition
- Oxidation
- Neutralisation
What is combustion?
- Combustion is a chemical reaction in which a substance is heated in the presence of oxygen to form one or more new substances. Heat and light are usually given out during combustion.
- Examples include the following chemical equations:
- Carbon + Oxygen → Carbon Dioxide (In the presence of heat)
- Sulfur + Oxygen → Sulfur Dioxide (In the presence of heat)
What is Thermal Decomposition?
- Thermal decomposition is a process in which a substance is broken down into two or more simpler substances upon heating.
Example:
1. Sugar → Carbon + Water Vapour (In the presence of heat)
2. Calcium Carbonate → Calcium Oxide + Carbon Dioxide (In the presence of heat)
What is Oxidation - Rusting?
Matter is able to interact with oxygen. When a substance gains oxygen, it undergoes a chemical change called oxidation.
Oxidation - Cellular Respiration
What is Cellular Respiration?
- Cellular Respiration is an oxidation reaction that occurs in the cells of living things.
- Matter is able to interact with oxygen. When a substance gains oxygen, it undergoes a chemical change called oxidation.
Example:
Glucose + Oxygen → Carbon Dioxide + Water
What is Neutralisation?
When an acid mixes with an alkali, a neutralisation occurs.
Characteristics of Acids
Hint: Taste, Effect on Objects, Litmus Paper, Reaction
- Sour Taste
- Corrosive (Some)
- Turns Blue Litmus Paper Red
- Reacts with Alkali, Metals and Carbonates
Characteristics of Alkali
Hint: Taste, Effect on Objects, Litmus Paper, Reaction
- Bitter Taste
- Soapy Feel
- Corrosive (Some)
- Turns Red Litmus Paper Blue
- Reacts with acid in neutralisation reactions.
Examples:
Baking Soda, Sodium Hydroxide, Ammonia, Potassium Hydroxide, Calcium Hydroxide
Word Equation for Neutralisation
Alkali + Acid → Salt + Water
* Toothpaste contains alkali, which neutralises the acid formed in our teeth by bacteria.
Example:
Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water
* The word “salt” is a general term for a compound containing an element that is a metal. E.g. salts containing the element
potassium include potassium chloride, potassium sulfate and potassium nitrate etc.
Word Equation for Acid & Metal Reaction
Acid + Metal → Salt + Hydrogen Gas
Example:
Hydrochloric Acid + Magnesium → Magnesium Chloride + Hydrogen Gas
* However, not all metals react with an acid in the same manner. Some metals (e.g. copper, silver, gold) do not react with acids.
What is the test and observation for Hydrogen Gas?
Test: Insert a lighted splint.
Observation: Colourless gas produced extinguishes a lighted splint with a ‘pop’ sound.
Word Equation for Acid & Carbonate Reaction
Acid + Carbonate → Salt + Carbon Dioxide Gas + Water
Examples:
Hydrochloric Acid + Calcium Carbonate → Calcium Chloride + Carbon Dioxide Gas + Water
What is the test and observation for Carbon Dioxide?
Test: Bubble the gas into limewater.
Observation: When the gas produced is bubbled into limewater, a white precipitate is formed on limewater.
What is the pH range for Acid, Alkali and Neutral?
- Solutions pH < 7 are acidic.
- Solutions pH> 7 are alkalinic.
- Solutions pH = 7 are neutral.
- The lower the pH value, the more acidic the solution.
- The higher the pH value, the alkaline the solution.
What is an Indicator?
An indicator is a substance which changes colour depending on whether the solution being tested is acidic or alkalinic.
Litmus Paper
In acids, what colour does the Red & Blue Litmus Paper turn into?
In alkali, what colour does the Red & Blue Litmus Paper turn into?
In Neutral Solution, what colour does the Red & Blue Litmus Paper turn into?
In acids, blue litmus paper turns red, and the red litmus paper remains red.
In alkali, blue litmus paper stays blue, and the red litmus paper turns blue.
In neutral solution, blue litmus paper stays blue, and the red litmus paper stays red.
What is Electrolysis?
Electrolysis is the chemical decomposition of substances with the passage of an electric current.
Example:
Water → (with electricity) Hydrogen + Oxygen
What is Electroplating?
Electroplating is the process in which a substance is coated with a metal with the passage of an electric current.
