Q5

• True or false? A hypothesis must be testable.

  True
• During a chemical reaction, is energy supplied or released when bonds are formed?

  Released

  Energy is released when new bonds are formed.
• True or false? A risk is a potential cause of harm, and the hazard is the chance it will cause harm

  False
• True or false? Exothermic reactions do not have an activation energy.

  False
• You want to measure the heat given off during four different reactions. Each of the reactions takes place in a flask with a lid. Why must each flask have a lid on?

  To contain the heat equally in each reaction

  The lid is needed to contain the heat equally in each reaction. If some flasks had a lid and some did not, the results would not be comparable.
• Professional sportspeople sometimes use special cooling packs as an alternative to ice packs after an injury. Are these packs based on an exothermic or an endothermic reaction?

  endothermic

  For the pack to become cool, the reaction has to be endothermic.
• Would the temperature of a reaction vessel during an endothermic reaction increase, decrease or stay the same?

  decrease

  The temperature would decrease. Endothermic reactions absorb energy from their surroundings. So energy from vessel would be absorbed during the reaction, which would decrease the temperature.
• A reaction has taken place, and as a result the mixture has cooled. What type of reaction has taken place?

  endothermic

  During an endothermic reaction, the temperature decreases.
• To investigate temperature change, you can react sodium hydroxide with hydrochloric acid. What salt is produced from this reaction?

  Sodium chloride

  Sodium hydroxide reacts to form sodium salts. Hydrochloric acid reacts to form chloride salts. The resulting salt is sodium chloride.
• To investigate temperature change, you can react sodium hydroxide with hydrochloric acid. What should you do to mix the solutions after you have poured them into a polystyrene cup?

  stir
• The apparatus shown in the diagram can be used to investigate temperature changes during chemical reactions. If the reaction was a neutralisation, would the temperature increase or decrease?

  increase

  Neutralisation is an exothermic reaction, so the temperature would increase.
• What is a control variable?

  It must be kept constant or at least monitored.