PAG 03: Enthalpy Determination Flashcards
What is calorimetry?
A process used to find the amount of energy released or used in a chemical reaction.
What type of reaction releases energy to surroundings?
Exothermic
What type of reaction takes in energy from surroundings?
Endothermic
What is a neutralisation reaction?
A reaction between an acid and a base, form a salt and water
What is meant by term enthalpy change of neutralisation?
The enthalpy change that accompanies the formation of 1 mole of water from a neutralisation reaction under standard conditions.
Write word and chemical equations for neutralisation reaction between sodium hydroxide and hydrochloric acid
Hydrochloric acid + sodium hydroxide -> sodium chloride + water
HCl + NaOH -> NaCl + H2O
The enthalpy change of a neutralisation reaction is being investigated. Why might this reaction be carried out in a styrofoam cup?
A styrofoam cup is a better thermal insulator than a glass beaker so the less heat will be lost to the surroundings meaning the calculated temperature change is more accurate
What equation is used to calculate energy absorbed by the solution?
Q= mc(temperature change)
m = mass of solution (g)
c = specific heat capacity
Q = heat energy (J)
How is the enthalpy change of neutralisation calculated from Q, the energy absorbed by solution?
Q / mol
number of moles can be calculated using mol= volume x concentration for hydrochloric acid used
How can you find maximum temperature reached during a neutralisation reaction?
Plot a graph of temperature (y axis) against time (x axis) and extrapolating to the time that the reactants were combined
Suggest 3 possible sources of error when investigating the enthalpy change of neutralisation. How could these errors be reduced?
- Heat transfer to and from surroundings
- Incomplete combustion if using fuel: could be used to combat these two errors
- Inaccuracy in temperature measurement: use an electronic thermometer
Describe an experiment to investigate enthalpy change of neutralisation of a reaction between hydrochloric acid and sodium hydroxide
- Add 25cm^3 HCl (aq) to a polystyrene cup. Place the cup in a glass beaker. Measure 25cm^3 NaOH (aq)
- Start timer. Record initial temperature of HCl at minute intervals for 3 minutes
- At the fourth minute, add the sodium hydroxide. Do not record the temperature.
- Continue recording temperature at minute intervals from 5 to 10 minutes. Stir solution when measuring temperature.
