Detailed notes on Unit 8 - Energetics I covering all the specification points, and allowed me to achieve an A* in chemistry. Covers enthalpy changes, thermochemical equations, Hess's law, Hess cycles, example calculations, standard enthalpy of formation, reaction, combustion, neutralisation and ato...
🔋
8-Energetics 1
Enthalpy Change
Thermochemical Equations
Hess’s Law
Standard Enthalpies
Standard Enthalpy of Reaction (ΔHr ⦵)
Practical: Calculation of Enthalpy of Reaction from an Experiment using an Insulated
Container
Standard Enthalpy of Combustion (ΔHc ⦵)
Practical: Experimental Method to Find the Enthalpy of Combustion of a Liquid
Calculation of Standard Enthalpy of Formation from Combustion
Standard Enthalpy of Neutralisation (ΔHne u t ⦵)
Practical: Experimental Method to find the Enthalpy of Neutralisation of an Acid
Standard Enthalpy of Atomisation (ΔHa ⦵)
Bond Enthalpy (ΔHB )
Calculation of Enthalpy of Reaction from Average Bond Enthalpies
Enthalpy Titrations
Law of Conservation of Energy - Energy can neither be
created nor destroyed, converted from one form to another.
Unit of energy - joule (J) or kilojoule (kJ).
8-Energetics 1 1
, Heat Transferred = Mass x Specific Heat Capacity x Temperature
Change
Q=mcΔT
Specific heat capacity of water - 4.18Jg− 1o C− 1 .
Specific Heat Capacity:
The energy required to increase the temperature of one gram of a substance by
one degree kelvin. Units - J K− 1 g− 1 .
Example:
Calculate the heat required to increase the temperature of 100cm3 of water from
17.6o C to 50.5o C.
ΔT = 50.5-17.6 = 32.9o C
Q=mcΔT
Q = 100 x 4.18 x 32.9
Q = 13,800J / 13.8kJ
Enthalpy Change
Enthalpy (H) of a system:
The enthalpy change (Δr H) for a reaction is the heat energy change measured
out under conditions of constant pressure.
The release or absorption of heat energy by a system at constant pressure
is caused by a change in the enthalpy of the chemicals.
Absolute enthalpy values cannot be found.
ΔH = (enthalpy of products) - (enthalpy of reactants).
ΔH = Hp - Hr
Heat Energy Change in a reaction (Q):
Can be measured experimentally using Q=mcΔT, where m is the mass of the
substance that has a temperature change ΔT and a specific heat capacity c.
Calorimetry:
8-Energetics 1 2
, The measurement of the heat required or absorbed by chemical reactions.
Exothermic Reactions:
Reactants have a higher enthalpy than the products.
The system loses energy during the reaction.
The value of ΔH is negative.
Energy is transferred to the surroundings as heat - surrounding increase in
temperature.
Endothermic Reactions:
Reactants have a lower enthalpy than the products.
The system gains energy during the reaction.
The value of ΔH is positive.
Energy is transferred from the surroundings as heat - surroundings decrease
in temperature.
Thermochemical Equations
Thermochemistry:
8-Energetics 1 3
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller thomaswong180805. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £2.99. You're not tied to anything after your purchase.
