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Volatile: Low boiling point liquid.
Bond energy: Energy needed to completely separate two bonded atoms.
Exothermic reaction: Reactions that release energy.
Endothermic reaction: Reactions that absorb energy.
Activation Energy: The minimum energy needed for a reaction to take place.
Activated Complex: The unstable transition state from reactants and products.
Enthalpy change ΔH: The energy absorbed or released in a chemical reaction.

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SYLLABUS (WHAT YOU NEED TO KNOW - CAPS):

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SYLLABUS (WHAT YOU NEED TO KNOW - CAPS):

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1. Energy Changes in Reactions:

Define heat of reaction (∆H) as the net change of chemical potential energy of the system.

Define exothermic reactions as reactions which release a net amount of energy, and transfer potential energy into thermal energy.

Define endothermic reactions as reactions which absorb a net amount of energy, and transfer thermal energy into potential energy.

Identify that bond breaking is endothermic and that bond formation is exothermic.

Identify that a stronger bond requires more energy to break and releases more energy when formed.

State that ∆H > 0 for endothermic reactions

State that ∆H < 0 for exothermic reactions

2. Calculations:

Do calculations of bond energies

3. Activation energy & activated complex:

Define activation energy as the minimum energy required to start a chemical reaction.

Colliding molecules must have THESE PROPERTIES before a reaction can take place:

the correct orientation,

a kinetic energy equal to or bigger than the activation energy of a reaction

Define the activated complex as a temporary transition state between the reactants and the products

4. Energy profiles:

Draw or interpret fully labelled sketch graphs (potential energy versus course of reaction graphs) of catalysed and uncatalysed endothermic and exothermic reactions (labeled with reactants, products, activation energy, activated complex and ∆H).

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DIFFERENCE BETWEEN THE CONCEPTS OF HEAT VS TEMPERATURE

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DIFFERENCE BETWEEN THE CONCEPTS OF HEAT VS TEMPERATURE

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What is the direction of heat flow between these blocks?

At which instance will heat flow stop?

T = measured in degrees Celsius or Kelvin.

Heat = measured in Joules.

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Bond breaking REQUIRES ENERGY (E taken in) = Endothermic process
Bond making RELEASES ENERGY (E given out) = Exothermic process

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BOND ENERGY = The amount of energy required to break a bond in one mole of the molecules in which the bond is formed, measured in kJ.mol-1

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BOND ENERGY = The amount of energy required to break a bond in one mole of the molecules in which the bond is formed, measured in kJ.mol-1

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Bond energy = The amount of energy required to break a bond in one mole of the molecules in which the bond is formed, measured in kJ.mol-1

A strong chemical bond would be a difficult bond to break.

Bond energy is therefore a measure of the strength of a bond.

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Exothermic Reaction:
A chemical reaction that transfers chemical potential energy into thermal energy where a net amount of energy is released.

Endothermic Reaction:
A chemical reaction that transfers thermal energy into chemical potential energy where a net amount of energy is absorbed.

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ENERGY PROFILES FOR ENDOTHERMIC VS EXOTHERMIC REACTIONS

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ENERGY PROFILES FOR ENDOTHERMIC VS EXOTHERMIC REACTIONS

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WHOOSH BOTTLE EXPERIMENT: Combustion of organic substances 🔥 (Professional Chemist)

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Another example of an endothermic reaction 

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Another example of an endothermic reaction 

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reaction of barium hydroxide and ammonium chloride

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ΔH = E in - E out

= Eabsorbed - Ereleased

= (435+243) - 2(431)

= 678 - 862

= -184 kJ/mol => EXOTHERMIC REACTION

Definition:

ΔH = The net change of chemical potential energy of a system during a chemical reaction, measured in kJ.mol⁻¹.

The overall (net) change of energy in a reaction shows:

how much energy must be supplied to reaction systems in order to keep the reaction going

or how much chemical potential energy will be released as thermal energy during a reaction

This change is known as the heat of reaction or enthalpy

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MAKING SUCCESSFUL COLLISIONS FOR REACTION

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MAKING SUCCESSFUL COLLISIONS FOR REACTION

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According to collision theory, a reaction will take place between two molecules, iff:

they collide with sufficiently high kinetic energy (to overcome the activation energy threshold).

the molecules have the correct orientation.

No reaction happens if 2 criteria above not met.

However, there is one way to make a reaction easier:

ADD A CATALYST!

Catalysts do not lower the activation energy, but they provide an alternative pathway with lower energy than the original activation energy

This will allow the reaction to take place quicker/easier.

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Catalyst DEFINITION:

A substance that speeds up the rate of a reaction by providing an alternative energy pathway with lower energy than the original activation energy of the reaction; it is not chemically changed by the end of the reaction.

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DEFINTION:

A substance that increases the rate of a reaction but remains itself unchanged at the end of the reaction.

A catalyst provides an alternative route of reaction with lower energy than the activation energy of the uncatalyzed reaction. So, more molecules have sufficient energy to undergo effective collisions.

Steps to catalysis:

Adsorption - reactants attach onto catalyst surface.

Alignment - reactant atoms align for effective overlap.

Desorption - products detach from catalyst.

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What Are Catalytic Converters | Environment | Chemistry | FuseSchool

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Think tank 15.1