Back to AI Flashcard MakerChemistry /A-level Chemistry: 3.1.4 Energetics Part 2
Describe how you can use a graph to find an accurate temperature change
During experiment, record temp at regular intervals
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Key Terms
Term
Definition
Describe how you can use a graph to find an accurate temperature change
During experiment, record temp at regular intervals
State what equation (& the units) you can use to calculate the enthaply change in calorimetry
State the equation used to calculate heat energy given out per mole
ΔH = q / moles of reaction
Define Hess's Law
Total enthalpy change of a reaction is independent of the route taken
What is Hess's law used for?
Working out enthaply changes that you can't find directly by doing an experiment
When working out enthalpies changes of formation, what data do you need?
ΔfH⦵ for all reactants and products that are compounds
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| Term | Definition |
|---|---|
Describe how you can use a graph to find an accurate temperature change | During experiment, record temp at regular intervals |
State what equation (& the units) you can use to calculate the enthaply change in calorimetry | |
State the equation used to calculate heat energy given out per mole | ΔH = q / moles of reaction |
Define Hess's Law | Total enthalpy change of a reaction is independent of the route taken |
What is Hess's law used for? | Working out enthaply changes that you can't find directly by doing an experiment |
When working out enthalpies changes of formation, what data do you need? | ΔfH⦵ for all reactants and products that are compounds |
Value of ΔfH⦵ for all elements = ____ | 0
(∵ element's being 'formed' from element = no change) |
What is bond enthalpy? | Energy required to break bonds |
Define mean bond enthalpy | Enthalpy heat (energy) change required to break a covalent bond on average across different compounds |
Draw the bonds between CO2 | |
Draw the bonds between NH3 | |
Draw the bonds between water | |
Draw the bonds between oxygen | |
Draw the bonds between nitrogen | |
Why are enthaply change values calculated from mean bond enthalpies less accurate than using Hess's Law? | ∵ use average values, enthalpy changes calculated using mean bond enthalpies aren't exact |
Using calorimetry to find the enthalpy of combustion of a flammable liquid Suggest 3 general improvements you can do to reduce errors due to heat loss |
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Explain why the bond enthalpy of a Cl-Cl bond is greater than that of a Br-Br bond (2) |
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