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Questions and Answers
Which material is typically a better conductor of electricity?
Which material is typically a better conductor of electricity?
When a solid is heated enough and changes into a liquid, this is an example of what type of change?
When a solid is heated enough and changes into a liquid, this is an example of what type of change?
Which of the following is a characteristic of a chemical reaction?
Which of the following is a characteristic of a chemical reaction?
What occurs when a gas is cooled sufficiently?
What occurs when a gas is cooled sufficiently?
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Which of the following is considered a permanent change?
Which of the following is considered a permanent change?
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Which of the following best describes thermal conductors?
Which of the following best describes thermal conductors?
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Photosynthesis in plants is an example of which type of change?
Photosynthesis in plants is an example of which type of change?
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Which material would most likely NOT be a good electrical conductor?
Which material would most likely NOT be a good electrical conductor?
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What type of change is melting an example of?
What type of change is melting an example of?
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Which of the following is NOT a characteristic of matter?
Which of the following is NOT a characteristic of matter?
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Which materials are considered thermal conductors?
Which materials are considered thermal conductors?
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What defines a chemical change compared to a physical change?
What defines a chemical change compared to a physical change?
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What are the three states of matter?
What are the three states of matter?
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Which of these materials is an insulator?
Which of these materials is an insulator?
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What process is described by the transformation of two substances into a completely new substance?
What process is described by the transformation of two substances into a completely new substance?
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Why is understanding material properties important for scientists and engineers?
Why is understanding material properties important for scientists and engineers?
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Study Notes
Materials: Properties and Changes
- Materials can change physically or chemically
- Physical changes alter the form, not composition (e.g., melting, cutting, freezing)
- Chemical changes create new substances (e.g., rusting, burning, cooking)
- Understanding material properties helps engineers and scientists create better technology
- Examples of materials: seawater, steel, copper, gold, silver, dry wood, diamond, oil, glass, rubber
Properties of Substances
- Matter is anything that has mass and takes up space (volume)
- Matter can change from solid to liquid to gas
- Materials are specific substances or combinations of substances (e.g., wood, marble)
- Substances are chemical elements (e.g., gold, water) or chemical compounds (e.g., water, salt)
Evaporation and Boiling
- Evaporation occurs at a fixed temperature
- Bubbles form throughout the liquid during evaporation
- Evaporation causes the liquid's temperature to decrease
- Evaporation is a faster process
- Boiling can occur at any temperature
- Boiling happens on the liquid's surface
- Temperature remains constant during boiling
- Boiling takes place until internal liquid temperature equals external temperature
Melting and Freezing
- Melting is changing from solid to liquid (reversible)
- Freezing is changing from liquid to solid (reversible)
- Melting and freezing have specific points for different materials
- Heat transfer between materials is called thermal conductivity
States of Matter
- Matter exists as solids, liquids, or gases
- Solids have fixed shapes and volumes
- Liquids take the shape of their container, but have fixed volume
- Gases spread to fill their container
Thermal and Electrical Conductors
- Thermal conductors allow heat to pass through them easily (e.g., metals)
- Insulators are poor conductors of heat (e.g., wood, plastic)
- Electrical conductors allow electricity to pass through them (e.g., metals)
- Insulators do not allow electricity to pass (e.g., wood, rubber)
Reversible Changes
- Some changes in materials can be reversed or undone (e.g., melting and freezing)
- Heating and cooling can cause changes in the state of substances
Irreversible Changes
- Changes that cannot be reversed or undone are called chemical reactions (e.g., burning, rusting)
- Chemical reactions result in new substances
Dissolving
- Dissolving occurs when a solid mixes with a liquid
- The liquid is called a solvent, the solid is the solute
- Dissolving forms a solution
- Solution particles are evenly spread within the solvent
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