C3.2 Energetics Flashcards
Define the term ‘activation energy’.
Activation energy is the minimum energy needed for a reaction to start.
During a chemical reaction, energy is transferred:
From the surroundings to break bonds in the reactants to form separate atoms
To the surroundings from the reacting particles when bonds form between atoms
What is an endothermic reaction?
When the temperature of the reaction mixture decreases during a chemical reactions
Energy is taken in from the surroundings
Describe the reaction profile for an exothermic reaction
In an exothermic reaction less energy is transferred to break the bonds than is transferred when new bonds form, so the energy change is negative and energy is transferred to the surroundings.
What is a reaction profile?
A reaction profile is a chart that shows the energy is involved.
Define the term ‘energy change’.
The energy change is the difference between th energy transferred from the surroundings to break bonds in the reactants, and the energy transferred to the surroundings when bonds form in the products.
What is an exothermic reaction?
When the temperature of the reaction mixture increases during a chemical reaction.
Energy is given out to the surroundings
Describe the reaction profile of an endothermic reaction
In an endothermic reaction, the amount of energy transferred to break the bonds is more than the energy transferred when new bonds form. This means that the energy change is positive. So the line for products is higher than the line for reactants in the reaction profile.
Define the term ‘bond energy’.
The energy needed to break 1 mol of a particular bond
Examples of exothermic reactions
Combustion, for example a fuel burning to cook food
Neutralisation, for example sodium hydroxide solution reacting with dilute hydrochloride acid.
Examples of endothermic reactions
The reaction between citric acid and sodium hydrogencarbonate in sherbet sweets, which is why they feel cold on your tongue.
Photosynthesis in plants, which involves carbon dioxide and water reacting to form sugars by using energy in light
