Changes of Matter and Chemical Reactions Flashcards

Fundamental Changes in Substances

• Definition of Change: A change is a transformation occurring in the physical or chemical properties of a substance.

• Types of Change:     - Physical Change: A change where the identity of the substance remains the same. Only its physical properties are altered, such as:         - Shape         - Size         - State         - Example: Melting of ice.     - Chemical Change: A change that leads to the formation of a new substance possessing different properties compared to the original.         - Example: Rusting of iron.

• Aqueous Solutions: An aqueous solution is one in which water serves as the solvent (the substance that dissolves another substance).

Chemical Reactions and Equations

• Chemical Reaction: A process in which a substance undergoes a transformation, resulting in the formation of new substances with different chemical properties.     - Example: Burning of paper ($\text{Paper} + \text{Oxygen} \rightarrow \text{Ash} + \text{Carbon dioxide}$).

• Chemical Equation: This represents a chemical reaction using symbols and formulas to denote the reactants and products involved.     - Example: $H_2 + O_2 \rightarrow H_2O$ ($\text{Hydrogen} + \text{Oxygen} \rightarrow \text{Water}$).

Characteristics of Chemical Reactions

• Indicators of a Reaction:     - Change in colour.     - Change in temperature.     - Change in state.     - Evolution of gas.     - Formation of precipitate.

• Temperature Changes (Thermal Reactions):     - Endothermic Reaction: A chemical reaction in which heat energy is absorbed.     - Exothermic Reaction: A chemical reaction that releases heat energy.

• Precipitate: An insoluble solid that settles down after the completion of a chemical reaction.

• Reactivity Trends:     - More reactive metals: Readily donate electrons.     - More reactive non-metals: Readily accept electrons.

• Catalyst: A substance that speeds up a chemical reaction or lowers the temperature/pressure needed to start one, without itself being consumed during the reaction.

Representation and Law of Conservation of Mass

• Conservation of Mass: This law ensures that the number of atoms of each element remains the same on both sides of a chemical equation.

• Principles:     - In a chemical reaction, mass is neither created nor destroyed.     - The mass of the reactant is equal to the mass of the product.

Essential Acids and Metal Interactions

• King of Acids: Sulphuric acid ($H_2SO_4$).

• Queen of Acids: Nitric acid ($HNO_3$).

• Reaction with Water: Whenever a metal reacts with water, it forms a metal hydroxide.

Types of Chemical Reactions

• 1. Combination (Synthesis) Reaction: A chemical reaction where two or more substances combine to form a single new substance ($A + B \rightarrow AB$).     - Combination of two elements: $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$.     - Combination of two compounds: $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}$.     - Combination of an element and a compound: $2SO_2(g) + O_2(g) \rightarrow 2SO_3(g)$.

• 2. Decomposition Reaction: A single compound breaks down into two or more simpler substances ($AB \rightarrow A + B$). This is usually caused by heat, light, or electricity.     - Thermolysis (Thermal Decomposition): A reaction where a compound breaks down when heated.         - Example: $2Pb(NO_3)_2(s) \xrightarrow{\Delta} 2PbO(s) + 4NO_2(g) + O_2(g)$.     - Electrolytic Decomposition: Electric current is used to decompose or break down compounds into constituent elements or ions.         - Example: $2H_2O(l) \xrightarrow{\text{Electricity}} 2H_2(g) + O_2(g)$.     - Photolytic Decomposition: Reactions initiated by exposure to light or sunlight.         - Example: $2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$.

• 3. Displacement Reaction: A reaction where a more reactive element replaces a less reactive element within its compound ($A + BC \rightarrow AC + B$).     - Types: Metal displacement, Non-metal displacement, or both.     - Example: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$.

• 4. Double Displacement Reaction: A reaction in which the cations and anions of two different compounds exchange places to form two new compounds ($AB + CD \rightarrow AD + CB$).     - Example: $Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq)$.     - Precipitate (Ppt) Reaction: A specific double displacement reaction where two aqueous ionic solutions react to form an insoluble solid that separates from the solution.

• Other Classifications Mentioned: Neutralization reaction and Gas evolution reactions.

Oxidation and Reduction (Redox)

• Oxidation: Refers to:     - The addition of oxygen: $C + O_2 \rightarrow CO_2$ (Oxidation of Carbon).     - The removal of hydrogen: $H_2S + Cl_2 \rightarrow 2HCl + S$ (Oxidation of Sulphur).     - The loss of electrons.     - The addition of an electronegative element.

• Oxidizing Agent: A substance that causes oxidation by accepting electrons; consequently, it gets reduced.

• Reduction: A chemical reaction involving:     - The addition of hydrogen: $N_2 + 3H_2 \rightarrow 2NH_3$ (Reduction of Nitrogen).     - The removal of oxygen.     - The removal of an electronegative element.

• Reducing Agent: A substance that brings about reduction. In the ammonia reaction above, $H_2$ is the reducing agent.

• Redox Reaction: A reaction where reduction and oxidation take place simultaneously.     - Example: $ZnO + C \rightarrow Zn + CO$.         - $ZnO$ is reduced (loses oxygen).         - $C$ is oxidized (gains oxygen).     - The substance getting oxidized acts as the Reducing Agent.     - The substance getting reduced acts as the Oxidizing Agent.

Corrosion of Metals

• Definition: Corrosion is the attack on a metal due to chemical reactions with substances like moisture, acids, and the environment.

• Standard Examples:     - Rusting of iron.     - Black coating on silver.     - Green coating on copper.

• Rusting of Iron (Specific Detail): Iron reacts with air and water to form iron rust, a reddish-brown flaky substance on the surface.

• Tarnishing of Silver: Silver reacts with oxygen and hydrogen sulfide in the air to form compounds that cause tarnishing.

• Harmful Effects:     - Damages iron structures.     - Weakens materials.     - Leads to heavy financial loss for repair and replacement.

• Preventive Measures:     - Painting.     - Galvanization.     - Oiling and greasing.     - Coating with non-reactive metals.

• Surface Impact: Rusting is fast on rough surfaces and slow on smooth surfaces.

Rancidity and Food Preservation

• Definition: Rancidity is the condition produced by the oxidation of fats and oils in food materials, resulting in a bad taste and unpleasant smell.

• Methods to Prevent Rancidity:     - Antioxidants: Chemical substances added to foods containing fat and oil to inhibit oxidation and prevent spoiling.     - Nitrogen Flushing: In chip packets, oxygen gas is replaced with nitrogen. Nitrogen is non-reactive and helps chips retain original taste and odor.     - Refrigeration: Storing food at low temperatures slows down oxidation, helping preserve taste and odor.

Supplementary Notes

• Oxygen Needs in Animals: Herbivores require more oxygen than carnivores because their plant-based diet is harder to digest and requires more energy for processing.

• Solution Characteristics:     - Dilute Solution: Low amount of solute, weak strength/effect.     - Concentrated Solution: High amount of solute, strong strength/effect.

• Functional Terms:     - Catalyst: Changes the speed of reaction but is not consumed.     - Electrolyte: A substance that allows electric current to pass through it.