Module 1 – Development of Practical Skills In Chemistry Flashcards
What is calorimetry?
Calorimetry is a process used to find the amount of energy released or used in a chemical reaction.
What type of reaction releases energy to the surroundings?
Exothermic
What type of reaction takes in energy from the surroundings?
Endothermic
What is a neutralisation reaction?
A reaction between an acid and a base, forming a salt and water.
What is meant by the term enthalpy change of neutralisation?
The enthalpy change that accompanies the formation of 1 mole of water from a neutralisation reaction under standard conditions.
What is the neutralisation reaction between hydrochloric acid and sodium hydroxide?
Hydrochloric acid + sodium hydroxide → sodium chloride + water
HCl + NaOH → NaCl + H2O
Why might a neutralisation reaction be carried out in a styrofoam cup?
A styrofoam cup is a better thermal insulator than a glass beaker, so less heat will be lost to the surroundings, making the calculated temperature change more accurate.
What equation is used to calculate the energy absorbed by the solution?
Q = mcΔT
Where: m - mass of the solution (g), c - specific heat capacity of the solution (the value for water is used), ΔT - temperature change (°C or K), Q - heat energy (J)
What does ‘m’ represent in the equation Q = mcΔT?
‘m’ represents the mass of the solution in grams (g).
What does ‘c’ represent in the equation Q = mcΔT?
‘c’ represents the specific heat capacity of the solution.
What does ‘ΔT’ represent in the equation Q = mcΔT?
‘ΔT’ represents the temperature change in degrees Celsius (°C) or Kelvin (K).
What does ‘Q’ represent in the equation Q = mcΔT?
‘Q’ represents the heat energy absorbed or released in joules (J).
How is the enthalpy change of neutralisation calculated?
Q ÷ mol
How can the number of moles be calculated?
mol = volume x concentration for the hydrochloric acid used
How can you find the maximum temperature reached during a neutralisation reaction?
Plot a graph of temperature (y axis) against time (x axis) and extrapolate to the time that the reactants were combined.
What are the possible sources of error when investigating the enthalpy change of neutralisation?
- Heat transfer to and from surroundings.
- Incomplete combustion if using fuel.
- Inaccuracy in temperature measurement.
How can the errors of heat transfer and incomplete combustion be reduced?
A bomb calorimeter could be used to combat these two errors.
How can inaccuracies in temperature measurement be reduced?
Use an electronic thermometer.
Describe an experiment to investigate the enthalpy change of neutralisation of a reaction between hydrochloric acid and sodium hydroxide
- Add 25cm3 HCl (aq) to a polystyrene cup. Place the cup in a glass beaker. Measure 25cm3 NaOH(aq).
- Start the timer. Record the initial temperature of the HCl at minute intervals for 3 minutes.
- At the fourth minute, add the sodium hydroxide and do not record the temperature.
- Continue recording the temperature at minute intervals from 5 to 10 minutes. Stir the solution when measuring the temperature.
What is a control variable?
A variable that is kept constant throughout the experiment
What is an independent variable?
A factor that is changed during the experiment to see the effect it has on another factor
What is a dependent variable?
A factor that is measured or observed in the experiment due to the changing of the independent variable
When plotting a graph what variables go on what axis?
The independent variable is on the x-axis
The dependent variable is on the y-axis
How do you measure the gradient of either a tangent or line of best fit?
Gradient = change in y-coordinate/change in x-coordinate