What is enthalpy a measure of?
The heat energy in a chemical system
The chemical system refers to the atoms, molecules, or ions making up the chemicals.
Can enthalpy be measured directly?
No
However, enthalpy changes can be measured.
What is the formula for enthalpy change (ΔH)?
ΔH = H(products) - H(reactants)
This formula indicates the difference in enthalpies between reactants and products.
ΔH can be positive or negative depending on what?
Whether the products contain more or less energy than the reactants
A positive ΔH indicates endothermic reactions, while a negative ΔH indicates exothermic reactions.
What does the law of conservation of energy state?
Energy cannot be created or destroyed
This fundamental rule of science applies to chemical reactions involving enthalpy changes.
In a chemical reaction, what is the system?
The chemicals - the reactants and products
The surroundings include everything that is not the chemical system.
What is an exothermic change?
Energy transfer from the system to the surroundings
This type of change releases heat.
What is an endothermic change?
Energy transfer from the surroundings to the system
This type of change absorbs heat.
What do enthalpy profile diagrams show?
The relative enthalpies of the reactants and products and the enthalpy change ΔH
These diagrams visually represent the energy changes during a reaction.
What is enthalpy a measure of?
The heat energy in a chemical system
The chemical system refers to the atoms, molecules, or ions making up the chemicals.
Can enthalpy be measured directly?
No
However, enthalpy changes can be measured.
What is the formula for enthalpy change (ΔH)?
ΔH = H(products) - H(reactants)
This formula indicates the difference in enthalpies between reactants and products.
ΔH can be positive or negative depending on what?
Whether the products contain more or less energy than the reactants
A positive ΔH indicates endothermic reactions, while a negative ΔH indicates exothermic reactions.
What does the law of conservation of energy state?
Energy cannot be created or destroyed
This fundamental rule of science applies to chemical reactions involving enthalpy changes.
In a chemical reaction, what is the system?
The chemicals - the reactants and products
The surroundings include everything that is not the chemical system.
What is an exothermic change?
Energy transfer from the system to the surroundings
This type of change releases heat.
What is an endothermic change?
Energy transfer from the surroundings to the system
This type of change absorbs heat.
What do enthalpy profile diagrams show?
The relative enthalpies of the reactants and products and the enthalpy change ΔH
These diagrams visually represent the energy changes during a reaction.
Why is there so many different types of enthalpy change of reaction?
For each reaction there are different conditions as each reaction is different, so scientists created specific tightly defined enthalpy changes where only one thing varies
What are the standard conditions?
Standard pressure is 100 kilopascals
Standard temperature is 298 k. 25 C.
Standard concentration is 1 moldm -3
Standard state is physical state of substance under standard condition
What is standard enthalpy change of reaction?
Enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions with all reactions and products in their standard States
What is enthalpy change of formation?
Standard enthalpy change of formation is enthalpy change that takes place when ONE mole of a compound is formed from its ELEMENTS under standard conditions
What is standard enthalpy change of combustion
Enthalpy change that takes place when ONE mole of a substance reacts COMPLETELY with oxygen under standard conditions
REACTS COMPLETELY SO PRODUCES CO2
What is standard enthalpy change of neutralisation?
Energy change that accompanies the reaction of an acid by a base to form mole of H2O liquid under standard conditions
- involves the reaction of H+ with oh minus both aqueous to form one mole of water liquid
