100% satisfaction guarantee Immediately available after payment Both online and in PDF No strings attached
logo-home
Summary notes for AQA A-Level Chemistry Unit 3.1.4 - Energetics $3.97   Add to cart

Summary

Summary notes for AQA A-Level Chemistry Unit 3.1.4 - Energetics

 12 views  0 purchase
  • Course
  • Institution
  • Book

Summary notes for AQA A-Level Chemistry Unit 3.1.4 - Energetics by an Imperial College London MSci Chemistry graduate. Notes divided into the following sections: Enthalpy Change, Calorimetry, Hess’s Law, Bond Enthalpies.

Preview 1 out of 3  pages

  • No
  • Chapter 4
  • June 11, 2023
  • 3
  • 2018/2019
  • Summary
avatar-seller
Section 1: Physical Chemistry

Energetics
Enthalpy Change
Enthalpy change (∆H): the heat energy change measured under conditions of constant pressure.
(Unit: kJ mol-1)
• Exothermic reactions give out energy to their surroundings, so the temp. in the reaction usually
goes up. The products of the reaction end up w/ less energy than the reactants. This means that the
enthalpy change for the reaction, ∆H, will be -ve.
• Endothermic reactions take in energy from their surroundings, so the temp. in the reaction usually
falls. The products of the reaction end up w/ more energy than the reactants. This means that the
enthalpy change for the reaction, ∆H, will be +ve.

Standard enthalpy values: the ∆H values for enthalpy changes of speci c reactions measured under
standard conditions.
• Standard conditions are represented by the symbol Ɵ.
- Standard conditions are 100 kPa (about 1atm) + 298K.
• State symbols should always be included in chemical equations to represent enthalpy changes.

Standard enthalpy change of reaction (∆rHƟ): the enthalpy change when a reaction occurs in the
molar quantities shown in the chemical equation, under standard conditions w/ all reactants +
products in their standard states.
• E.g. CaO(s) + H2O(l) → Ca(OH)2(s)

Standard enthalpy change of formation (∆fHƟ): the enthalpy change when 1 mole of a compound is
formed from its constituent elements in their standard states under standard conditions.
• E.g. 2C(s) + 3H2(g) + ½O2(g) → C2H5OH(l)
The enthalpy change of formation of an element is zero if the element is in its standard state. E.g. the
enthalpy of formation of oxygen, O2(g) , is zero.

Standard enthalpy change of combustion (∆cHƟ): the enthalpy change when 1 mole of a substance is
completely burned in oxygen under standard conditions w/ all reactants + products in their standard
states.
• E.g. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
• ∴ if for the above equation, ∆cHƟ = -890kJ mol-1 , then for the equation below…
2CH4(g) + 4O2(g) → 2CO2(g) + 4H2O(l)
… the enthalpy change for the reaction is ∆rHƟ = 2 x ∆cHƟ = -1780kJ

Calorimetry
Experiments that measure the heat given out by reactions.are called calorimetry experiments.

For reactions that happen in solution…
Put the reactants (w/ a known conc./mass) in a polystyrene cup (to reduce
heat loss or gain through the sides), that is in a beaker (for stability). Use a
thermometer to measure the temp. of the mixture at regular intervals. Stir
the solution to make sure it’s evenly heated.

For combustion reactions…
Energy given out by a combustion reaction can be calculated by measuring the temperature change it
causes as it burns. To nd the enthalpy of combustion of a ammable liquid, you burn it in a
calorimeter, as seen in the diagram:





fi fl fi

The benefits of buying summaries with Stuvia:

Guaranteed quality through customer reviews

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

Quick and easy check-out

You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.

Focus on what matters

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 bookishresearcher. Stuvia facilitates payment to the seller.

Will I be stuck with a subscription?

No, you only buy these notes for $3.97. You're not tied to anything after your purchase.

Can Stuvia be trusted?

4.6 stars on Google & Trustpilot (+1000 reviews)

85443 documents were sold in the last 30 days

Founded in 2010, the go-to place to buy study notes for 14 years now

Start selling
$3.97
  • (0)
  Add to cart