Chapter 9 Flashcards
What is Enthalpy?
(H) Is the measure of heat energy PRESENT in a chemical system.
What is Enthalpy Change?
(/\H) Is the amount of energy released/taken in during a chemical reaction.
What’s an Endothermic Reaction?
(+/\H) A reaction which takes in energy from the surroundings.
What’s an Exothermic Reaction?
(-/\H) A reaction that releases energy into the surroundings.
What’s the Law of “Conservation Of Energy,” ?
Conservation of energy is one of the fundamental rules of science which states that energy cannot be created or destroyed.
What happens when a chemical reaction takes place involving Enthalpy change?
When a chemical reaction takes place, involving enthalpy change, HEAT ENERGY is transferred between the chemical system and the surroundings.
What happens to endothermic and exothermic reactions in terms of the chemical system and the surroundings?
In an EXOTHERMIC reaction, the chemical system releases heat energy into the surroundings. Any energy lost from the chemical system is balanced by the energy gained by the surroundings. The temp of the surroundings Increases as energy gain increases.
In an ENDOTHERMIC reaction, the chemical system takes in heat energy from the surroundings. Any energy lost from the surroundings Is balanced by the energy gained by the chemical system. The temp of the surroundings will decrease as the energy loss increases.
What is activation energy and its symbol?
(Ea) Activation energy is the minimum energy required to break bonds to allow a chemical reaction to take place.
What happens in chem reactions involving Ea?
Atoms and Ions are held together by chemical bonds. During a chemical reaction, the bonds in the reactants need to be broken by an input of energy to be turned into products.
EA acts as an energy barrier to a reaction.
In general, which level of Activation energy is preferred and why? Small or Large.
Reactions with Smaller activation energy will take place rapidly because the energy required to break the bonds is readily available from the surroundings.
What is Standard Conditions?
What is meant by Standard state?
`Can Vary depending on the conditions used.
Pressure= 101kPa Temperature= 298K (25*) Concentration= 1moldm-3
Standard state relates to the physical state of a substance under standard conditions.
What is the Enthalpy Change Of Reaction and what does it depend on?
(/\rH) Is the enthalpy change associated with the stated equation in the molar quantities shown in the chemical equation under standard conditions.
Always depends on the balancing numbers in a stated equation.
What is the Standard Enthalpy change of Formation?
What is it’s rule for elements?
(/\fH) Is the enthalpy change associated with the formation of 1 mole of a compound from its elements under standard conditions with all its reactants and products in their standard states.
The /\fH for an element will always be 0 as no chemical change is taking place.
What is the Standard Enthalpy Change of Combustion?
What are the products when a substance completely reacts with Oxygen?
(/\cH) Is the enthalpy change associated with the complete combustion of 1 mole of a substance under standard conditions with all the reactants and products in their standard states.
Products of complete combustion will always be H2O and CO2.
What is the Standard Enthalpy Change of Neutralisation?
(/\nH) Is the enthalpy change associated with the formation of 1 mole of water from a neutralisation reaction between an acid and base under standard conditions with all reactants and products in their standard states.
The value of (/\nH) is the same for all neutralisation reactions.
