Podcast
Questions and Answers
Which of the following is an example of a physical change?
Which of the following is an example of a physical change?
- Burning wood
- Cooking an egg
- Melting ice (correct)
- Rusting of iron
What type of change alters the form or appearance of a substance but does not change its chemical composition?
What type of change alters the form or appearance of a substance but does not change its chemical composition?
- Physical change (correct)
- Chemical change
- Ionic change
- Nuclear change
What is the process of a solid changing directly into a gas called?
What is the process of a solid changing directly into a gas called?
- Freezing
- Melting
- Sublimation (correct)
- Condensation
Which of the following is a sign of a chemical change?
Which of the following is a sign of a chemical change?
In a chemical equation, what are the substances on the left side of the arrow called?
In a chemical equation, what are the substances on the left side of the arrow called?
What type of reaction involves a substance reacting rapidly with oxygen to produce heat and light?
What type of reaction involves a substance reacting rapidly with oxygen to produce heat and light?
Which of the following factors usually increases the rate of a chemical reaction?
Which of the following factors usually increases the rate of a chemical reaction?
What principle states that mass is neither created nor destroyed in a chemical reaction?
What principle states that mass is neither created nor destroyed in a chemical reaction?
Which of the following is a physical property of a substance?
Which of the following is a physical property of a substance?
Flashcards
Physical Change
Physical Change
Alterations that do not change the chemical identity of a substance, often involving changes in size, shape, or state. The chemical formula remains the same and are often reversible.
Melting
Melting
The change from a solid to a liquid state.
Freezing
Freezing
The change from a liquid to a solid state.
Boiling
Boiling
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Condensation
Condensation
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Sublimation
Sublimation
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Chemical Change
Chemical Change
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Combination (Synthesis) Reactions
Combination (Synthesis) Reactions
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Decomposition Reactions
Decomposition Reactions
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Exothermic Reactions
Exothermic Reactions
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Study Notes
- Physical and chemical changes are fundamental concepts describing matter alteration.
- Physical changes affect a substance's form without changing its chemical composition.
- Chemical changes rearrange atoms and molecules, forming new substances.
Physical Changes
- These do not alter the chemical identity of a substance.
- They often involve changes in size, shape, or state.
- Examples: changes of state (melting, freezing, boiling, condensation, sublimation), tearing, crushing, dissolving.
- The chemical formula remains constant during a physical change.
- Physical changes are often reversible.
States of Matter
- Matter exists as solid, liquid, gas, and plasma.
- Transitions between these states are physical changes.
- Melting: solid to liquid at the melting point.
- Freezing: liquid to solid at the freezing point.
- Boiling: liquid to gas at the boiling point.
- Condensation: gas to liquid.
- Sublimation: solid directly to gas.
- Deposition: gas directly to solid.
Dissolving
- This is a physical change where a solute disperses in a solvent.
- The solute's chemical identity remains unchanged.
- Example: Sugar (C12H22O11) dissolving in water remains sugar molecules surrounded by water.
- The process is reversible through evaporation.
Chemical Changes
- Also known as chemical reactions, they rearrange atoms and molecules to form new substances.
- These are typically irreversible without further reactions.
- Indicators: color change, gas formation, precipitate formation, heat absorption (endothermic) or release (exothermic), and light emission.
- Examples include burning, rusting, cooking, and neutralization reactions.
- Reactants convert into products during these.
Chemical Equations
- These represent chemical reactions.
- Reactants are on the left, products on the right, separated by an arrow.
- Example: 2H2 + O2 → 2H2O (hydrogen gas + oxygen gas forms water).
- Balancing ensures the number of atoms of each element is the same on both sides.
Types of Chemical Reactions
- Combination (Synthesis): A + B → AB
- Decomposition: AB → A + B
- Single Displacement: A + BC → AC + B
- Double Displacement: AB + CD → AD + CB
- Combustion: a substance reacts rapidly with oxygen, producing heat and light.
- Acid-Base Neutralization: an acid reacts with a base to form a salt and water.
Evidence of Chemical Changes
- Color Change: indicates a new substance.
- Gas Formation: bubbles indicate gas release (not boiling).
- Precipitate Formation: a solid forming when two solutions are mixed.
- Heat Absorption or Release: endothermic cools, exothermic heats.
- Light Emission: strong indicator of a chemical reaction.
Examples of Physical Changes
- Melting ice: solid to liquid water (H2O).
- Boiling water: liquid to steam (H2O).
- Chopping wood: changes size and shape, remains wood.
- Dissolving salt in water: salt disperses, retains original properties.
- Bending a metal rod: changes shape, same composition.
Examples of Chemical Changes
- Burning wood: forms ash, carbon dioxide, and water.
- Rusting of iron: forms iron oxide.
- Cooking an egg: proteins denature and solidify.
- Baking a cake: reactions produce new compounds.
- Neutralizing acid with a base: HCl + NaOH → NaCl + H2O.
Factors Affecting the Rate of Chemical Reactions
- Temperature: Higher temperature increases reaction rate.
- Concentration: Higher concentration generally increases reaction rate.
- Surface Area: Increased surface area increases reaction rate.
- Catalysts: speed up reactions without being consumed.
- Pressure: Increasing pressure can increase reaction rate for gases.
Conservation of Mass
- Mass is neither created nor destroyed in a chemical reaction.
- Total reactant mass equals total product mass.
- Essential for balancing equations.
- During physical changes, mass remains constant.
Energy Changes
- Chemical reactions involve energy changes.
- Exothermic reactions release energy, decreasing the system's energy.
- Endothermic reactions absorb energy, increasing the system's energy.
- Enthalpy change (ΔH) quantifies energy change: negative for exothermic, positive for endothermic.
Physical vs. Chemical Properties
- Physical properties: observed without changing chemical identity (color, density, melting point, boiling point).
- Chemical properties: describe reactions with other substances (flammability, reactivity with acids, oxidizing ability).
- Physical changes alter physical properties, and chemical changes alter chemical properties.
Applications in Daily Life
- Crucial in cooking, cleaning, industrial processes, and environmental science.
- Cooking: melting butter (physical), and baking a cake (chemical).
- Cleaning products: uses chemical reactions to remove stains.
- Industrial processes: manufacturing plastics and pharmaceuticals depend on reactions.
- Environmental science: used to understand pollution and climate change.
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Description
Explore physical and chemical changes, focusing on alterations to matter. Physical changes affect form without altering chemical composition, while chemical changes create new substances by rearranging atoms and molecules. Learn about states of matter and their transitions.