3.1 Changes of State & The Particle Model

• What is density defined as?

  The mass per unit volume of a material

  
• How does the density of low density materials compare to high density materials?

  Low density materials have a low mass
• Why is a bag full of feathers lighter than a similar bag full of metal?

  Feathers have a lower density than metal
• Why is a balloon less dense than a small bar of lead?

  It occupies a larger volume with less mass
• How is density related to mass and volume?

  Density = mass / volume

  
• Why are gases less dense than solids?

  Molecules in gases are more spread out
• What is the formula triangle for density, mass, and volume?

  Density, mass, volume triangle

  
• What units are used for density when mass is in grams and volume in cm³?

  Density will be in g/cm³
• What happens if a material is more dense than water?

  It will sink in water
• What is the density of water?

  1000 kg/m³
• How does the density of air compare to that of water?

  Air is significantly less dense than water
• What is the density of air at sea level and room temperature?

  1.3 kg/m³
• Why are gases highly compressible?

  There are large gaps between the particles
• What are the characteristics of solids, liquids, and gases?

  • Solids:
  • Closely packed particles
  • Fixed shape and volume
  • Liquids:
  • Closely packed particles
  • No fixed shape, definite volume
  • Gases:
  • Widely spaced particles
  • No fixed shape or volume

  
• How do particles behave in a solid?

  They vibrate about fixed positions
• How do particles behave in a liquid?

  They can flow over one another
• How do particles behave in a gas?

  They move randomly and are far apart
• What is the difference in density between solids and liquids?

  They are roughly the same density
• Why do gases have significantly lower densities than solids or liquids?

  Molecules in gases are widely separated
• What is the distance between molecules in a gas compared to solids or liquids?

  About ten times greater

  
• How does the density of a gas compare to that of a solid or liquid?

  Typically around one-thousandth of a solid

  
• What is the method for measuring the density of regularly shaped objects?

  1. Measure mass using a digital balance
  2. Measure dimensions with a ruler or calipers
  3. Calculate volume based on shape
  4. Use density formula to find density
• What is the resolution of a digital balance?

  0.01 g
• What is the first step in measuring density of irregularly shaped objects?

  Use a displacement technique
• What are the variables in the density measurement experiments?

  • Independent variable: Type of shape/volume
  • Dependent variable: Mass of the object
• What should you remember when converting units for density calculations?

  Convert larger units to smaller by multiplying
• What is the relationship between mass, weight, and density?

  Mass is amount of matter; weight is force
• How can you visualize density at the atomic level?

  Consider particles in a cubic centimetre
• What happens to the volume of steam compared to liquid water?

  Steam occupies a greater volume than water
• Why is it important to consider both mass and volume in density?

  Density is defined by both mass and volume

  
• What is the formula for calculating density?

  ρ = m / V

  
• How do you convert from centimetres to metres?

  Divide by 100
• What is the significance of significant figures in density calculations?

  To ensure precision in measurements
• What is the importance of averaging measurements in experiments?

  To reduce errors and improve accuracy
• What is the purpose of using a displacement technique for irregular objects?

  To measure volume indirectly
• What is the first step in calculating the density of an object?

  Measure its mass
• What should you do after measuring the mass of an object?

  Measure its dimensions
• What is the final step in determining density after measuring mass and volume?

  Use the density formula

  
• Why is it important to repeat measurements in experiments?

  To ensure reliability of results
• What is the significance of rounding the density answer to two significant figures?

  To maintain precision in reporting