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Year 8 Revision

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  • In which type of substance are atoms of different elements chemically bonded together?
    In compounds
  • Name the subatomic particle labelled 'E' in the image.
    Neutron
  • Can you name five common signs of a chemical change, other than a new substance being produced?
    heat/light produced; solid produced (precipitate); gas produced, causing bubbling or fizzing; odour produced; permanent colour change
  • How does the kinetic energy of particles differ between solids, liquids and gases?
    The kinetic energy of particles is highest in gases and lowest in solids.
  • Apart from its volume, what increases when a solid expands?
    The distance between particles
  • What causes a solid to melt?
    Heating the solid increases the kinetic energy of particles until they have enough kinetic energy to overcome some of the attraction between them.
  • In which state of matter are the attractive forces between particles extremely weak?
    Gas
  • In which section(s) of this heating curve is the kinetic energy of particles increasing?
    Sections A, C and E
  • Does the image show a physical change or a chemical reaction?
    Chemical reaction
  • In which state of matter are the particles unable to flow?
    Solid
  • Why does carbon have the atomic number 6?
    Each carbon atom has 6 protons in its nucleus.
  • If a gas in a rigid container is heated, what increases?
    The pressure inside the container (as the gas particles collide more forcefully with the walls of the container)
  • Which of the pictured materials consists of identical molecules? How do you know?
    A and D, because they each contain identical particles consisting of multiple atoms chemically bonded together
  • Which change of state involves a gas becoming a liquid?
    Condensation
  • Which phase change involves a solid changing directly into a gas?
    Sublimation
  • Name the part labelled 'B' in the image.
    Nucleus (atomic nucleus)
  • What causes freezing?
    Removing heat decreases the kinetic energy of particles, which allows attractive forces between them to pull them into a rigid structure.
  • In which section(s) of this heating curve is all the added energy being used to break forces of attraction between particles?
    Sections B and D
  • What is the type of energy that is associated with an object or particle in motion?
    Kinetic energy
  • What must be broken for water to undergo a chemical reaction? Refer to the image.
    Covalent bonds between oxygen and hydrogen atoms
  • In which section of this heating curve is the kinetic energy of particles too low to overcome attractive forces between them?
    Section A
  • Name 5 elements!
    Many possible answers (see the periodic table)
  • Do solids expand or contract when heated? Why?
    They expand because the kinetic energy of the particles is increasing, pushing them farther apart and increasing the space between them.
  • Which of the pictured materials is a mixture? How do you know?
    C, because it contains multiple types of particles (and thus contains multiple pure substances)
  • Does the image show a physical change or a chemical reaction?
    Physical change
  • Which type of change is usually reversible?
    Physical change
  • Does the image show a physical change or a chemical reaction?
    Physical change (change of state)
  • Which of the pictured materials are elements? How do you know?
    B and D, because they each contain only one type of atom
  • What is happening at the part of the heating curve labelled '2'? Why?
    The substance is melting. The temperature is not increasing because the added heat is being used to break attractive forces between particles.
  • Based on the image, in which type of chemical reaction are there fewer reactants than products?
    Decomposition
  • Why is a gas less dense than a solid?
    The particles in a gas are closer together
  • Do liquids expand or contract when cooled? Why?
    They contract, because the decrease in kinetic energy of particles allows the attractive forces between them to pull them closer together.
  • Explain why 1 litre of water is heavier than 1 litre of oil.
    Water is denser than oil
  • What MUST happen for a chemical reaction to have occurred?
    A new substance must have been produced.
  • Why is a solid incompressible?
    Because the particles in a solid are very close together
  • What increases when you heat a gas in a deflated balloon? Why?
    The volume of the balloon increases because the particles are moving faster and colliding more forcefully with the sides of the balloon.
  • Magnesium gives off a very bright white light when it burns in the presence of oxygen. Is this an example of a chemical property or a physical property?
    Chemical property
  • Are particles moving fastest in the solid state, the liquid state, or the gaseous state?
    Gaseous state
  • Which of the pictured materials is a compound? How do you know?
    A, because it contains atoms of two different elements joined by chemical bonds
  • Can any of these compounds be in the solid state when iodine is a gas? Justify your answer.
    Sodium chloride, sodium carbonate and sugar can be in the solid state when iodine is a gas, because they each have a MP that is greater than iodine's BP.
  • Based on the image, how do we know that rusting is a chemical reaction?
    Because iron oxide has a different chemical composition from iron (the atoms are arranged differently).
  • Give two examples of physical changes in which heat is absorbed.
    melting; evaporation; boiling
  • Which state of matter has a fixed volume but no fixed shape?
    Liquid
  • The image on the left shows ice and the the image in the middle shows liquid water. Based on the image, what is unusual about water compared to most other substances?
    In its solid state, water molecules are further apart than in the liquid state. Usually, the opposite is true.
  • Explain the ideal physical properties of a rover designed to explore volcanoes on Jupiter. (Refer to melting point, density, and strength.)
    High melting point, low density, high strength
  • Identify a difference between evaporation and boiling.
    Evaporation occurs at all temperatures, and only at the liquid surface, whereas boiling occurs only at the boiling point and throughout the whole liquid.
  • Why do atoms have no overall charge?
    The number of protons is equal to the number of electrons.
  • For melting to occur, does energy have to be added to a substance or removed from the substance?
    Added
  • For which substance is the heating curve shown? How do you know?
    Water, because of its melting point and boiling point
  • Name a type of reaction in which the mass of products is greater than the mass of reactants. Explain your choice.
    This is not possible. In chemical reactions, the mass of products equals the mass of reactants due to the law of conservation of mass.
  • Which type of substance contains only one type of atom?
    Elements
  • Which change of state involves a liquid transforming into a gas at the liquid surface?
    Evaporation
  • Is any of these compounds a gas at room temperature? Justify your answer.
    Methane is a gas at room temperature, because it boils at a temperature below room temperature.
  • To convert water to pure hydrogen and pure oxygen, what must be broken?
    Chemical bonds between atoms
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