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Topic 3 module 1 questions

School of Chemistry
Questions – Thermochemistry
Dr Stuart Thickett
Question 1.
Identify the following systems as open, closed or isolated: (a) a space shuttle rocket
booster; (b) hot coffee in a perfectly insulated pot.
Question 2.
A piece of silver of mass 363 g has a heat capacity of 85.7 JoC-1. What is the specific
heat capacity of the silver?
Question 3.
Burning a 1.500 g sample of methane, CH4, in a bomb calorimeter increases the
temperature of the calorimeter by 2.190 oC. The enthalpy of combustion of methane
is − 890.3 kJ mol-1. Calculate the heat capacity of the calorimeter in kJ/oC.
Question 4.
When 2.266 g of an unknown compound is burned in the same calorimeter, the
temperature of the calorimeter increases by 1.059 oC. Calculate the heat of
combustion of the unknown compound in kJ g-1.
Question 5.
A piece of Cu of mass 19.0 g at 87.4 °C was placed in a calorimeter containing
55.5 g of water at 18.3 °C. The final temperature was 20.4 °C. Calculate the specific
heat capacity of the Cu.
Question 6.
Consider the reaction,
2 CH3OH(l) + 3 O2(g) → 4 H2O(l) + 2 CO2(g)
ΔH = -1452.8 kJ.
What is the value of ΔH if:
Question 7.
The equation is multiplied throughout by 2?
The direction of the reaction is reversed so that the products become
the reactants and vice versa?
Water vapour instead of liquid water is formed as a product? (Provide a
qualitative answer only, will ΔH increase or decrease?)
Define Hess’s Law and the standard enthalpy of formation
Question 8 .
Nitromethane, CH3NO2, is a good fuel. It is a liquid at room temperature. When the
liquid is burned, the reaction involved is:
2 CH3NO2(l) + 1½ O2(g) → 2 CO2(g) + N2(g) + 3 H2O(l)
The standard enthalpy of formation of liquid nitromethane at 25 oC is -112 kJ mol-1.
Using the following information:
the enthalpy of formation of CO2(g) is -393.5 kJ mol-1
the enthalpy of formation of H2O(l) is -285.8 kJ mol-1
Calculate the enthalpy change in the burning of 5 moles of liquid nitromethane to
form products at 25 oC. Comment on the magnitude of the result obtained and state
whether the reaction is exothermic or endothermic.
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