Unit 3 - Lesson 14: Measuring Enthalpy Change Flashcards
What do we need to know to calculate enthalpy change (ΔH)?
The amount of heat energy lost or gained in a reaction. Exothermic reactions will emit heat and endothermic will absorb heat.
What is calorimetry used for?
Calorimetry is used to measure the change in temperature during a reaction.
What do we call change in temperature?
ΔT. The delta (Δ) means ‘change in’ and T represents temperature.
What does calorimetry involve?
Calorimetry involves measuring the temperature of the reactants before a reaction and then the temperature of the products after. The difference between the two is ΔT.
What is calorimetry used to measure ΔT for? (What kind of reactions?)
Halogen displacement, dissolving and neutralisation reactions in solution.
Calorimetry is used to measure the energy transferred during a neutralisation reaction between hydrochloric acid and sodium hydroxide. True or false? Memorise this.
True. Calorimetry is used to measure the energy transferred during a neutralisation reaction between hydrochloric acid and sodium hydroxide.
What is the chemical equation for a neutralisation reaction between hydrochloric acid and sodium hydroxide?
HCl (hydrochloric acid) + NaOH (sodium hydroxide) → NaCl + H2O
Calorimetry is used to measure the energy transferred during a neutralisation reaction between hydrochloric acid and sodium hydroxide. What is the method for this?
b) What are the advantages of using a polystyrene cup?
c) What can be added to increase insulation?
- Put 25cm^3 of HCl and NaOH in separate beakers.
- Add the HCl followed by the NaOH to a polystyrene cup with a lid. The polystyrene cup should be in a beaker filled with cotton wool for insulation.
- Take the temperature of the mixture every 30 seconds and record the highest temperature.
b) The polystyrene cup is an insulator so minimises heat loss.
c) Aluminium foil can be added to increase insulation further.
Calorimetry is used to measure the energy transferred during an ethanol combustion reaction. What is the chemical formula and method for this?
Chemical Formula: C2H5OH + 3O2 → 2CO2 + 3H2O
Method:
1. Measure out 50-100cm^3 of water using a measuring cylinder (precise). Pour in to a copper can (copper is a good conductor of heat).
2. Take the initial temperature of water.
3. Weigh a spirit burner containing ethanol with its lid on (so no alcohol evaporates).
4. Arrange the apparatus as shown with a shield to prevent draughts.
5. Burn fuel until the water reaches 40 degrees Celsius. Measure maximum temperature & reweigh spirit burner.
What do combustion reactions ALWAYS require?
A fuel. For example, ethanol and oxygen (O2) in air.
Provide pictures of/draw:
a) Calorimetry is used to measure the energy transferred during a neutralisation reaction between hydrochloric acid and sodium hydroxide.
b) Calorimetry is used to measure the energy transferred during an ethanol combustion reaction.
a)https://i.pinimg.com/736x/df/4b/85/df4b85c8bd8e4a97c465932ac181b4a0.jpg
b)https://i.pinimg.com/736x/76/6f/32/766f329fa896e1423c3503d137270b8c.jpg
Select the reactions where calorimetry could be used to measure ΔT:
a) Combustion
b) Neutralisation
c) Halogen Displacement
d) Dissolving Solutes In Solution
All of them: A, B, C & D
During combustion calorimetry, screens act as draught excluders to minimise heat loss to the surroundings. True or false?
True
The amount of energy transferred in a halogen displacement reaction can be measured using calorimetry. Fill in the missing product from this halogen displacement reaction:
Cl2 + 2I^- → 2Cl^- + ?
Cl2 + 2I^- → 2Cl^- + I2
The amount of energy transferred in a neutralisation reaction can be measured using calorimetry. Fill in the missing product from this neutralisation reaction.
H2SO4 + ZnO –> ? + H2O
H2SO4 + ZnO –> ZnSO4 + H2O
The amount of energy transferred in a neutralisation reaction can be measured using calorimetry. Fill in the missing product from this neutralisation reaction.
2HNO3 + MgO –> ? + H2O
2HNO3 + MgO –> Mg(NO3)2 + H2O
Abigail adds 25cm3 of HCl and 25cm3 of CuO to a polystyrene cup. She takes the temperature of the mixture every 30 seconds and records the highest temperature.
Abigail is carrying out calorimetry. What products can she expect?
CuCl2 + H2O
Ahmed performs calorimetry on chlorine water (Cl2) with potassium bromide solution (KBr). What colour will the mixture turn in the cup?
HINT: This is a halogen-displacement reaction.
Orange
Why is copper a good material to use during calorimetry of combustion reactions?
It is a good conductor of heat.
