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QLDChemistryQuick questions
Unit 1: Chemical fundamentals (structure, properties and reactions)
Quick questions on Exothermic and endothermic reactions, enthalpy and calorimetry (QCE Chemistry Unit 1)
15short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is exothermic versus endothermic?Show answer
The system is the chemicals undergoing reaction. The surroundings are everything else (the calorimeter, the water, the air). When the system releases heat, the surroundings warm up; when the system absorbs heat, the surroundings cool down.
What is enthalpy and bond energy?Show answer
The first-order explanation of Delta H is bond energetics:
What is energy profile diagrams?Show answer
A reaction profile plots potential energy (y-axis) against reaction progress (x-axis). Five features to label:
What is calorimetry?Show answer
A calorimeter measures the heat exchanged between a reaction and a defined mass of water (or, in a bomb calorimeter, a fully closed system). For QCE Chemistry Unit 1 the standard apparatus is a simple polystyrene-cup calorimeter, or a spirit burner heating a beaker of water.
What is converting q to molar enthalpy of reaction?Show answer
1. Calculate q in J using q = mcDeltaT. 2. Convert to kJ by dividing by 1000.
What is sources of error in school calorimetry?Show answer
A QCAA-grade IA evaluation expects you to identify systematic and random errors:
What is standard enthalpy changes (selected)?Show answer
A standard enthalpy change is measured at 25 degrees C and 100 kPa with reactants and products in their standard states.
What is connecting to later units?Show answer
Unit 2 builds collision theory and activation energy onto this framework. Unit 3 introduces Hess's law and enthalpy of formation for indirect Delta H calculations (in some QCAA schools), and reuses enthalpy in the context of equilibrium. Unit 4 connects enthalpy with the energetics of combustion fuels and biofuels.
What is catalyst?Show answer
A catalyst provides an alternative path with a lower transition state, so a lower E_a. Delta H is unchanged.
What is reversible reaction?Show answer
Both forward and reverse activation energies can be drawn. Forward E_a minus reverse E_a equals Delta H (with sign).
What is forgetting the sign on Delta H?Show answer
Negative for exothermic. The water heating up means the reaction lost heat; Delta H is negative.
What is forgetting to convert mL to g?Show answer
When given a volume of solution, multiply by density (often 1.00 g/mL for dilute aqueous) to get mass.
What is mixing Delta H with q?Show answer
q is the heat exchanged in a specific experiment (joules); Delta H is the molar enthalpy in kJ/mol. Divide q by moles to get Delta H.
What is treating Delta T as a temperature, not a change?Show answer
Delta T = T_final - T_initial. A 20 degrees C rise is the same in degrees C and K.
What is treating the calorimeter as perfectly insulating?Show answer
Always mention heat loss when evaluating a school experiment; a high-quality answer quantifies the percent captured.