Science Essay questions

• Explain the factors that affect the rate of a chemical reaction regarding enzymes and/or sparks that can ignite wood.

  Reactant concentration, the physical state of the reactants, and surface area, temperature, and the presence of a catalyst are the four main factors that affect reaction rate.
• describe the differences between synthesis, decomposition and replacement reactions

  Precipitation reactions involve the formation of one or more insoluble products. A synthesis reaction is a type of chemical reaction in which two or more simple substances combine to form a more complex product. A decomposition reaction is a type of chemical reaction in which one reactant yields two or more products.
• know how the Law of Conservation of Mass relates to the balancing equation. 


  A balanced chemical equation always obeys law of conservation of mass. According to this law the mass of products must be equal to the mass of reactants. A reaction is said to be balanced when the total mass of atoms on both sides of the chemical reaction is equal.
• Elements

  Substances that cannot be broken down into simpler substances by chemical means
• Compounds

  Substances made up of two or more different elements chemically bonded together
• Chemical reaction

  A process in which some substances, called reactants, change into different substances, called products
• Chemical reaction

  1. Bonds break in reactants

  2. New bonds form in products
• Types of chemical reactions

  • Synthesis
  • Decomposition
  • Replacement
  • Combustion
• All chemical reactions involve energy
• Exothermic reactions

  Release more energy than they use
• Endothermic reactions

  Use more energy than they release
• Be able to describe whether a reaction is endothermic or exothermic, and be able to explain this in terms of the energy of reactants and products, as shown by the graphs in the textbooks. 


  When energy is released in an exothermic reaction, the temperature of the reaction mixture increases. When energy is absorbed in an endothermic reaction, the temperature decreases.