Energetics Test Term 1 , 1.0

• What is an exothermic reaction?


  Heat energy is given out to the surroundings, resulting in an increase in temperature.
• What are two examples of exothermic reactions?


  Combustion and neutralisation.
• What is an endothermic reaction?


  Heat energy is taken in from the surroundings, causing a decrease in temperature.
• What are two examples of endothermic reactions?


  Thermal decomposition and photosynthesis.
• What is calorimetry used for?


  • To measure the amount of heat energy involved in a chemical reaction.
• What is the method for measuring heat in combustion reactions?


  Burn a substance and measure the heat transferred to water.
• How is heat measured in displacement reactions?


  Mix a more reactive metal with a solution of a less reactive metal's salt.
• What is the method for measuring heat in dissolving reactions?


  Dissolve a solid in water and measure the temperature change.
• How is heat measured in neutralisation reactions?


  Mix an acid and an alkali, recording the temperature change.
• What is the formula for calculating heat energy change?


  • \( Q = mc\Delta T \)
  • \( Q \): Heat energy change (joules)
  • \( m \): Mass of water/solution (in grams)
  • \( c \): Specific heat capacity of water (usually \( 4.18 \, \text{J/g/°C} \))
  • \( \Delta T \): Change in temperature (°C)
• How do you calculate the heat energy change during an experiment?


  Use the formula \( Q = mc\Delta T \) where you measure mass, specific heat capacity, and temperature change.
• What does \( \Delta H \) represent in a reaction?


  • Enthalpy change per mole of substance involved in the reaction.
  • A negative \( \Delta H \) indicates an exothermic reaction.
  • A positive \( \Delta H \) indicates an endothermic reaction.
• What is the formula for calculating molar enthalpy change (\( \Delta H \))?


  \( \Delta H = \frac{Q}{n} \)
• What does \( Q \) represent in the molar enthalpy change formula?


  Heat energy change (in Joules).
• What does \( n \) represent in the molar enthalpy change formula?


  Number of moles of reactant.
• What are the temperature changes in different types of reactions?


  • Salts dissolving in water: Can be exothermic or endothermic.
  • Neutralisation reactions: Generally exothermic, releasing heat.
  • Displacement reactions: Usually exothermic.
  • Combustion reactions: Strongly exothermic.
• What is relative atomic mass (Ar)?


  Mass of an atom of an element compared to carbon-12.
• What is relative formula mass (Mr)?


  The sum of all the relative atomic masses (Ar) of the atoms in a compound.
• What is the relative formula mass of water (H₂O)?


  18
• What is the mole (mol)?


  The unit for the amount of a substance.
• How many particles are in one mole of any substance?


  1. 02 × 10²³ particles (Avogadro's number).
• What is the mass of one mole of a substance in grams?


  It is its relative formula mass (Mr).
• How do you calculate the amount of substance in moles?


  • Amount of substance (mol) = Mass (g) / Mr
• If you have 10g of NaCl (Mr = 58.5), how many moles of NaCl do you have?


  0.171 mol.
• What are the steps for reacting mass calculations?


  1. Write the balanced chemical equation.
  2. Use the mole ratio to find the ratio of reactants to products.
  3. Calculate the moles of the known substance using its mass and Mr.
  4. Use the mole ratio to find the moles of the unknown substance.
  5. Calculate the mass of the unknown substance using its Mr and the moles calculated.
• In the reaction \( H_2 + Cl_2 \rightarrow 2HCl \), if you have 2g of \( H_2 \), how do you calculate the mass of \( HCl \) produced?


  Use the balanced equation and mole ratios to find the mass of \( HCl \).
• What is the formula for percentage yield?


  Percentage yield = \( \frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100 \)
• What is the actual yield in a chemical reaction?


  The amount of product obtained from the reaction.
• What is the theoretical yield in a chemical reaction?


  The maximum possible amount of product based on the reactants.