Changes of state

• What do cookies provide according to the text?

  The best online experience
• What is the particle model used to explain?

  The properties of substances in their different states and changes of state
• What are the common changes of state summarized in the diagram?

  • Melting
  • Evaporation
  • Boiling
  • Sublimation
• What is sublimation?

  When a solid turns straight into a gas without becoming a liquid
• What is an example of a substance that can sublime?

  Solid carbon dioxide ('dry ice')
• What must be transferred for changes of state to happen?

  Energy must be transferred by heating
• What is evaporation?

  A change of state from liquid to gas
• How do particles behave during melting?

  Particles gain energy to break some of the bonds between them
• What happens to particles during evaporation?

  Particles gain energy to overcome forces of attraction
• What is the difference between evaporation and boiling?

  Evaporation occurs at the surface, while boiling forms bubbles throughout the liquid
• What determines the amount of energy needed to change state?

  The strength of the forces between the particles of a substance
• What is the melting point?

  The temperature at which a solid changes into a liquid
• What is the boiling point?

  The temperature at which a substance rapidly changes from a liquid to a gas
• How do the strength of forces between particles affect melting and boiling points?

  The stronger the forces, the higher the melting and boiling points
• How do the forces between ions in an ionic solid compare to those in water?

  The forces between ions in an ionic solid are stronger than those between molecules in water
• What are the melting and boiling points of sodium chloride, water, and hydrogen?

  • Sodium chloride: Melting point 801°C, Boiling point 1413°C
  • Water: Melting point 0°C, Boiling point 100°C
  • Hydrogen: Melting point -259°C, Boiling point -252°C
• Can evaporation occur below the boiling point of a substance?

  Yes, evaporation can take place below the boiling point
• What happens to energy when a substance condenses or freezes?

  Energy is transferred from the substance to the surroundings
• How can the state of a substance at a given temperature be predicted?

  By knowing its melting point and boiling point
• What are the predicted states of a substance based on temperature?

  • Temperature < melting point: Solid
  • Temperature between melting and boiling points: Liquid
  • Temperature > boiling point: Gas
• What is the predicted state of oxygen at -200°C if its melting point is -218°C and boiling point is -183°C?

  Oxygen will be in the liquid state
• What is a limitation of the particle model?

  The particle model assumes particles are solid spheres with no forces between them
• Why are particles not considered solid spheres in the particle model?

  Because atoms are mostly empty space
• What is true about the shape of many particles?

  Many particles are not spherical