26 terms

iGCSE Chemistry: Energetics - test myself

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What is meant by the term endothermic?
A reaction in which heat energy is taken in (surroundings get colder)
What is meant by the term exothermic?
A reaction in which heat energy is given out (surroundings get hotter)
Explain why experimental values of enthalpy change differ from theoretical values
Heat energy is lost to the surroundings. Not all the reactants are used up.
In a calorimetry experiment to investigate the heat energy released by the combustion of ethanol, why should the water in the calorimeter be stirred?
To ensure the heat energy is mixed evenly throughout all the water
Use Q=mcΔT and c=4.18J/°C/g. 25cm³ of sulfuric acid is put into a boiling tube. The starting temperature is 21°C. A spatula of iron filings is added. After a while the temperature reaches 33°C. What is the total heat energy change?
1254 J
Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?
-355 J
Use Q=mcΔT and c=4.18J/°C/g. A strip of magnesium is added to a beaker with 200cm³ of copper (II) sulfate. The temperature starts at 21.7°C and rises to a maximum of 23.1°C. What is the total heat energy change?
1170 J
In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.
738 kJ/mol
State the units of molar enthalpy change.
kJ/mol
(Triple only) Draw an energy level diagram for an endothermic reaction and use ΔH to represent the enthalpy change
(Triple only) Draw an energy level diagram for an exothermic reaction and use ΔH to represent the enthalpy change
(Triple only) What does the symbol ΔH mean
enthalpy (energy) change
(Triple only) Explain, in terms of making and breaking bonds, why a reaction could be endothermic
The energy need to break the bonds is more than the energy released to make the bonds
(Triple only) Explain, in terms of making and breaking bonds, why a reaction could be exothermic
The energy need to break the bonds is less than the energy released to make the bonds
(Triple only) In an endothermic reaction, which takes more energy: the breaking of bonds or the making of new bonds?
Breaking bonds
(Triple only) In an exothermic reaction, which takes more energy: the breaking of bonds or the making of new bonds?
Making new bonds
(Triple only) Is breaking bonds exothermic or endothemic?
Endothermic
(Triple only) Is making new bonds exothermic or endothemic?
Exothermic
(Triple only) Assuming bond energies in kJ/mol: H-C 412, C-C 348, O-H 463, C-O 360, C=C 612. Calculate the molar enthalpy change for the reaction: ethanol → ethene + water
+45 kJ/mol
(Triple only) In a chemical reaction, 250 kJ/mol is taken to break all the bonds and 280 kJ/mol is released when new bonds are formed. What is the overall molar enthalpy of the reaction?
-30 kJ/mol
(Triple only) In a chemical reaction, the overall molar enthalpy is +87 kJ/mol. Is this reaction exothermic or endothermic?
Endothermic
(Triple only) In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?
Exothermic
Are combustion reactions exothermic or endothermic?
Exothermic
Are displacement reactions exothermic or endothermic?
Exothermic
Are neutralisation reactions exothermic or endothermic?
Exothermic
When a solid dissolves, is this process exothermic or endothermic?
Endothermic