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THERMOCHEMISTRY chemical-reaction-exothermic-reaction-energy…
THERMOCHEMISTRY
Heat
Is thermal energy transferred from a hotter system to a cooler system that are in contact.
It is represented by "q".
It is a PROCESS.
Temperature
Is a measure of the average kinetic energy of the atoms or molecules in the system.
It is related to an instrument called thermometer.
It is a MEASURE.
Internal energy
It is separated in scale from the macroscopic energy associated with moving objects.
It is composed of 2 types of energy
KINETIC ENERGY
It is the motion of particles inside an object.
2 types
Vibrational and rotational kinetic energy
Refers to the energy produced by the movement of vibration and rotation a bond between 2 atoms has.
Translational kinetic energy
Refers to the energy produced by the movement of particles from one place to another.
POTENTIAL ENERGY
The attraction between the particles in an object.
It is produced
intermolecular forces
What are they?
Forces produced by the interaction between molecules.
3 tyes
London Forces
Is a basic force between all molecules
means that is present in all interactions.
It explains the interaction (attraction) between non-polar molecules.
Dipole-Dipole forces
Is the attraction and repulsion between polar molecules.
Ion - Dipole Forces
The interaction between ions and polar molecules.
Hydrogen bonds
or
Hydrogen bridges
Is a type of Dipole-Dipole interaction
between molecules that have
2 more items...
It is defined as the energy associated with the random, disordered motion of molecules.
Example
A room temperature glass of water sitting on a table has no apparent kinetic or potential energy
on the microscopic scale it is a seething mass of high speed molecules traveling at hundreds of meters per second.
It refers to the invisible microscopic energy on the atomic and molecular scale.
Microscopic energy
Monoatomic gas
Only translational kinetic energy
Liquid
&
Solid
2 types of kinetic energy
Potential energy
Polyatomic gas
2 types of kinetic energy
Specific heat
What is it?
The energy required to increase 1 degree the temperature of 1 gram of substance.
It depends on the internal energy each substance has.
Example
Water needs more specific heat to increase 1 degree than Copper because its intermolecular force is stronger.
System
It refers to the chemical reaction that is taking.
Surroundings
It refers to everything else in the universe.
Enthalpy changes (ΔH)
What it is?
Is the amount of heat energy taken in/given out in a chemical reaction.
We can measure it when the system moves from an initial state to some final state.
2 reactions
Exothermic reaction
The heat energy is transferred from the system to the surroundings.
the surroundings get hotter.
ΔH will always be negative.
The products are at a lower energy level than the reactants
they are more stable than the reactants.
Formula
ΔH = enthalpy of products - enthalpy of reactants
total energy of the reactants = total energy of the products + heat given
Example
methane burning in oxygen
CH4(g) + 2O2 --> CO2(g) + 2H2O(l) ΔH = -890 kJ mol-1
Endothermic reaction
The system takes in heat energy from the surroundings
the surroundings get cooler.
ΔH will always be positive
The products have a higher energy than the reactants
they are less stable than the reactants.
Formula
ΔH = enthalpy of products - enthlapy of reactants
total energy of the reactants = total energy of the products + heat taken in
Example
the reaction between nitrogen and oxygen to form nitrogen (II) oxide
N2 + O2(g) --> 2NO(g) ΔH= + 181 kJ mol-1
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