Physical Chemistry 3.2 Flashcards
(24 cards)
What is enthalpy?
It is the thermal energy that is stored in a chemical system (H)
What is a system?
It is the actual reaction (the atoms and bonds involved)
What is the surroundings?
It is everything else
What are the standard conditions (Θ)?
- 100 KPa
- 298K
What is the law of conservation of energy?
Energy cannot be created or destroyed only transferred from one place to another
What is enthalpy change?
Heat exchange with the surroundings during a chemical reaction at a constant pressure and the difference between enthalpy of the products and reactants
What is the symbol equation of standard enthalpy change?
∆H = H(products) - H(reactants)
What is activation energy?
It is the minimum energy required to start a reaction by breaking the bonds in the reactants
What is the enthalpy change of reaction? (∆rHΘ)
The energy change associated with a given reaction under standard conditions
What is the enthalpy change of formation? (∆fHΘ)
The energy change that takes place when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions
What is the enthalpy change of combustion? (∆cHΘ)
The energy change that takes place when 1 mole of a substance is completely combusted under standard conditions
What is the enthalpy change of neutralisation? (∆neutHΘ)
The energy change associated with the formation of 1 mole of water from neutralisation under standard conditions
What is chemical energy?
A special form of potential energy that lies within chemical bonds
What happens in an exothermic reaction?
- the enthalpy of products is smaller than the reactants enthalpy
- heat loss from the chemical system
- enthalpy change has a negative symbol
What happens in an endothermic reaction?
- enthalpy of the products is greater than the enthalpy of the reactants
- heat gain to the chemical system
- enthalpy change has a positive sign
Explain exothermic reactions in terms of bond breaking and making
It takes more energy to break the bonds that it does to make them
Explain endothermic reactions in terms of bond breaking and making
It takes more energy to make the bonds than it does to break them
What is the expression used for calorimetry?
q= mc∆T
What does q mean in calorimetry?
The heat exchanged with the surroundings (J)
What does m mean in calorimetry?
Mass of the substance heated or cooled (g) (use the volume of the liquid)
What does c mean in calorimetry?
The specific heat capacity of the substance being heated or cooled ( J/gK)
What does T mean in colorimetry?
The change in temperature (K)
What is calorimetry?
The quantitative study of energy in a chemical reaction
Is energy needed to make or break bonds?
Energy is needed to break bonds
