Enthalpy Changes Flashcards
(12 cards)
Use ideas about the enthalpy changes that take place during bond breaking and bond making to explain why some reactions are exothermic
Bond breaking absorbs energy and bond making releases energy. More energy is released than absorbed.
If the products of a reaction is carbon dioxide and water, what name is given to this oxidation process in the body?
Respiration
If the products in a reaction is glucose and oxygen, what is the name of the oxidation process in the body?
Photosynthesis
What is the equation to work out energy released?
q = m x c x T(change in temperature)
Suggest two reasons why standard enthalpy changes of combustion determined experimentally are less exothermic than the calculated theoretical values
- Heat is released to surroundings
- Non-standard conditions
State Le Chatelier’s principle
The position of equilibrium will shift, minimising the effect of any change in conditions and counteracting the change
Define the term enthalpy change of combustion
The enthalpy change when one mole of substance is burnt in excess oxygen under standard conditions (100kPa and 25 degrees C)
What are the standard condition?
100kPa and 25 degrees C
It is very difficult to determine the standard enthalpy change of formation of hexane directly. Suggest a reason why.
- Many hydrocarbons would form
- Activation energy is too high
Why do bond enthalpies have positive values?
Bond breaking is endothermic so energy has to be put in to break the bond
Define the term enthalpy change of formation
The enthalpy change when one mole of compound is formed from its elements under standard conditions (100kPa and 25 degrees C)
What are the conditions indicated by the circle with the line through it?
Standard conditions meaning 100kPa and 25 degrees C
