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Chemical Substances, Reactions and Essential Resources(WJEC)
1. Chemical Reactions Overview
Chemical Reaction Definition:
A process where reactants are transformed into products through the breaking and forming of chemical bonds.
Evidence of a Chemical Reaction:
Formation of Gas: Bubbling or odor change.
Formation of a Precipitate: A solid that forms from a solution.
Color Change: Indicates a new substance is formed.
Temperature Change: Exothermic (releases heat) or Endothermic (absorbs heat).
Emission of Light: Energy release in the form of light.
Chemical Equation:
Representation: Reactants→Products
Balancing: Law of Conservation of Mass - Atoms are neither created nor destroyed.
2. Types of Chemical Reactions
Synthesis Reaction: A synthesis reaction occurs when two or more simple substances combine to form a more complex substance.
Decomposition Reaction: A decomposition reaction occurs when a single compound breaks down into two or more simpler substances.
Single Replacement Reaction: A single replacement reaction occurs when one element replaces another element in a compound, forming a new compound and a different element.
Double Replacement Reaction: A double replacement reaction occurs when parts of two ionic compounds are exchanged, making two new compounds.
Combustion Reaction: A combustion reaction occurs when a substance reacts with oxygen, releasing energy in the form of light or heat, and forming oxides.
3. Reaction Kinetics
Factors Affecting Reaction Rates:
Concentration: Higher concentration usually increases reaction rate.
Temperature: Higher temperature typically increases reaction rate.
Surface Area: More surface area increases reaction rate.
Catalysts: Substances that increase the reaction rate without being consumed.
Inhibitors: Substances that decrease the reaction rate.
Activation Energy:
Minimum energy required for reactants to form products.
Catalyst Function:
Lowers activation energy, increasing the rate of reaction.
4. Energy in Chemical Reactions
Exothermic Reactions:
Release energy (heat).
Products have less energy than reactants.
Example: Combustion of glucose
Endothermic Reactions:
Absorb energy (heat).
Products have more energy than reactants.
Example: Photosynthesis
Enthalpy (ΔH):
Heat content of a system.
Exothermic: ΔH<0
Endothermic: ΔH>0
Entropy (ΔS\Delta SΔS):
Measure of disorder.
Higher entropy: More disorder.
Lower entropy: Less disorder.
Gibbs Free Energy (ΔG):
Determines spontaneity of a reaction.
ΔG=ΔH−TΔS
Spontaneous: ΔG<0
Non-Spontaneous: ΔG>0
5. Equilibrium in Chemical Reactions
Dynamic Equilibrium:
Rate of forward reaction equals rate of reverse reaction.
Concentrations of reactants and products remain constant over time.
Le Chatelier’s Principle:
If a system at equilibrium is disturbed, the system adjusts to minimize the disturbance.
Factors Affecting Equilibrium:
Concentration: Adding/removing reactants/products shifts equilibrium.
Temperature: Increasing temperature favors endothermic reactions; decreasing temperature favors exothermic reactions.
Pressure (Gases): Increasing pressure favors the side with fewer moles of gas.
6. Periodic Table structure
7. Ionic Compounds
8. Mixtures and Separation Technique:
A mixture is a combination of two or more substances where each substance retains its individual chemical properties. Mixtures can be homogeneous or heterogeneous.
Types of Mixtures:
Homogeneous Mixture (Solution): Composition is uniform throughout.
Example: Salt dissolved in water.
Heterogeneous Mixture: Composition is not uniform; different parts of the mixture are visibly distinct.
Example: Sand mixed with iron filings.
1. Filtration
Filtration is a technique for separating an insoluble solid from a liquid or gas.
This process involves pouring the mixture through a filter paper or another porous material.
The solid particles are trapped on the filter, while the liquid or gas passes through. Filtration is commonly used to purify liquids by removing solid impurities, such as separating sand from water.
Equipment typically includes filter paper and a funnel. It’s a basic and widely used method for solid-liquid separations in both household and industrial applications.
2. Evaporation
Evaporation separates a soluble solid from a liquid by heating the mixture until the liquid evaporates, leaving the solid residue behind.
The principle relies on the difference in boiling points between the solvent and the solute. During the process, the solution is heated in an evaporating dish, causing the liquid to turn into vapor, while the solid remains.
This method is used for obtaining substances like salt from seawater or concentrating solutions.
It's a straightforward technique essential in both laboratory settings and large-scale salt production.
3. Chromatography
Chromatography is used to separate and analyze different components in a mixture based on their movement through a stationary phase and a mobile phase.
The process involves placing a small spot of the mixture on chromatography paper, which is then placed in a solvent.
As the solvent moves up the paper by capillary action, different components travel at different speeds and separate.
Chromatography is widely used in laboratories for analyzing complex mixtures, such as separating pigments in ink or testing food additives. It’s crucial for qualitative analysis in chemistry and biology.
4. Distillation
Distillation is a method for separating components in a liquid mixture based on differences in their boiling points.
It involves heating the mixture in a distillation flask until the more volatile component vaporizes. The vapor is then condensed back into a liquid in a condenser and collected in a receiving flask.
Distillation can be simple, for separating substances with widely different boiling points, or fractional, for closer boiling points.
This technique is essential for purifying liquids, such as producing distilled water or separating ethanol from water in chemical processes.
9. Percentage Mass and Yield:
Percentage mass (or mass percent) quantifies the concentration of an element in a compound or a component in a mixture, expressed as a percentage of the total mass. It is calculated using the formula:
Percentage yield measures the efficiency of a chemical reaction, comparing the actual yield (amount of product obtained) to the theoretical yield (maximum possible amount based on stoichiometric calculations). It is calculated using the formula:
Chemical Substances, Reactions and Essential Resources(WJEC)
1. Chemical Reactions Overview
Chemical Reaction Definition:
A process where reactants are transformed into products through the breaking and forming of chemical bonds.
Evidence of a Chemical Reaction:
Formation of Gas: Bubbling or odor change.
Formation of a Precipitate: A solid that forms from a solution.
Color Change: Indicates a new substance is formed.
Temperature Change: Exothermic (releases heat) or Endothermic (absorbs heat).
Emission of Light: Energy release in the form of light.
Chemical Equation:
Representation: Reactants→Products
Balancing: Law of Conservation of Mass - Atoms are neither created nor destroyed.
2. Types of Chemical Reactions
Synthesis Reaction: A synthesis reaction occurs when two or more simple substances combine to form a more complex substance.
Decomposition Reaction: A decomposition reaction occurs when a single compound breaks down into two or more simpler substances.
Single Replacement Reaction: A single replacement reaction occurs when one element replaces another element in a compound, forming a new compound and a different element.
Double Replacement Reaction: A double replacement reaction occurs when parts of two ionic compounds are exchanged, making two new compounds.
Combustion Reaction: A combustion reaction occurs when a substance reacts with oxygen, releasing energy in the form of light or heat, and forming oxides.
3. Reaction Kinetics
Factors Affecting Reaction Rates:
Concentration: Higher concentration usually increases reaction rate.
Temperature: Higher temperature typically increases reaction rate.
Surface Area: More surface area increases reaction rate.
Catalysts: Substances that increase the reaction rate without being consumed.
Inhibitors: Substances that decrease the reaction rate.
Activation Energy:
Minimum energy required for reactants to form products.
Catalyst Function:
Lowers activation energy, increasing the rate of reaction.
4. Energy in Chemical Reactions
Exothermic Reactions:
Release energy (heat).
Products have less energy than reactants.
Example: Combustion of glucose
Endothermic Reactions:
Absorb energy (heat).
Products have more energy than reactants.
Example: Photosynthesis
Enthalpy (ΔH):
Heat content of a system.
Exothermic: ΔH<0
Endothermic: ΔH>0
Entropy (ΔS\Delta SΔS):
Measure of disorder.
Higher entropy: More disorder.
Lower entropy: Less disorder.
Gibbs Free Energy (ΔG):
Determines spontaneity of a reaction.
ΔG=ΔH−TΔS
Spontaneous: ΔG<0
Non-Spontaneous: ΔG>0
5. Equilibrium in Chemical Reactions
Dynamic Equilibrium:
Rate of forward reaction equals rate of reverse reaction.
Concentrations of reactants and products remain constant over time.
Le Chatelier’s Principle:
If a system at equilibrium is disturbed, the system adjusts to minimize the disturbance.
Factors Affecting Equilibrium:
Concentration: Adding/removing reactants/products shifts equilibrium.
Temperature: Increasing temperature favors endothermic reactions; decreasing temperature favors exothermic reactions.
Pressure (Gases): Increasing pressure favors the side with fewer moles of gas.
6. Periodic Table structure
7. Ionic Compounds
8. Mixtures and Separation Technique:
A mixture is a combination of two or more substances where each substance retains its individual chemical properties. Mixtures can be homogeneous or heterogeneous.
Types of Mixtures:
Homogeneous Mixture (Solution): Composition is uniform throughout.
Example: Salt dissolved in water.
Heterogeneous Mixture: Composition is not uniform; different parts of the mixture are visibly distinct.
Example: Sand mixed with iron filings.
1. Filtration
Filtration is a technique for separating an insoluble solid from a liquid or gas.
This process involves pouring the mixture through a filter paper or another porous material.
The solid particles are trapped on the filter, while the liquid or gas passes through. Filtration is commonly used to purify liquids by removing solid impurities, such as separating sand from water.
Equipment typically includes filter paper and a funnel. It’s a basic and widely used method for solid-liquid separations in both household and industrial applications.
2. Evaporation
Evaporation separates a soluble solid from a liquid by heating the mixture until the liquid evaporates, leaving the solid residue behind.
The principle relies on the difference in boiling points between the solvent and the solute. During the process, the solution is heated in an evaporating dish, causing the liquid to turn into vapor, while the solid remains.
This method is used for obtaining substances like salt from seawater or concentrating solutions.
It's a straightforward technique essential in both laboratory settings and large-scale salt production.
3. Chromatography
Chromatography is used to separate and analyze different components in a mixture based on their movement through a stationary phase and a mobile phase.
The process involves placing a small spot of the mixture on chromatography paper, which is then placed in a solvent.
As the solvent moves up the paper by capillary action, different components travel at different speeds and separate.
Chromatography is widely used in laboratories for analyzing complex mixtures, such as separating pigments in ink or testing food additives. It’s crucial for qualitative analysis in chemistry and biology.
4. Distillation
Distillation is a method for separating components in a liquid mixture based on differences in their boiling points.
It involves heating the mixture in a distillation flask until the more volatile component vaporizes. The vapor is then condensed back into a liquid in a condenser and collected in a receiving flask.
Distillation can be simple, for separating substances with widely different boiling points, or fractional, for closer boiling points.
This technique is essential for purifying liquids, such as producing distilled water or separating ethanol from water in chemical processes.
9. Percentage Mass and Yield:
Percentage mass (or mass percent) quantifies the concentration of an element in a compound or a component in a mixture, expressed as a percentage of the total mass. It is calculated using the formula:
Percentage yield measures the efficiency of a chemical reaction, comparing the actual yield (amount of product obtained) to the theoretical yield (maximum possible amount based on stoichiometric calculations). It is calculated using the formula:
