Difference between revisions of "Exothermic"
(→Key Stage 4) |
(→Examples) |
||
| Line 36: | Line 36: | ||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
| − | | style="height:20px; width: | + | | style="height:20px; width:100px; text-align:center;" |'''Bond''' |
| − | | style="height:20px; width: | + | | style="height:20px; width:150px; text-align:center;" |'''Energy in kJ/mol''' |
|- | |- | ||
| − | | style="height:20px; width: | + | | style="height:20px; width:100px; text-align:center;" |C-H |
| − | | style="height:20px; width: | + | | style="height:20px; width:150px; text-align:center;" |413 |
|- | |- | ||
| − | | style="height:20px; width: | + | | style="height:20px; width:100px; text-align:center;" |O=O |
| − | | style="height:20px; width: | + | | style="height:20px; width:150px; text-align:center;" |498 |
|- | |- | ||
| − | | style="height:20px; width: | + | | style="height:20px; width:100px; text-align:center;" |O-H |
| − | | style="height:20px; width: | + | | style="height:20px; width:150px; text-align:center;" |464 |
|- | |- | ||
| − | | style="height:20px; width: | + | | style="height:20px; width:100px; text-align:center;" |C=O |
| − | | style="height:20px; width: | + | | style="height:20px; width:150px; text-align:center;" |799 |
|} | |} | ||
Revision as of 14:59, 14 January 2019
Contents
Key Stage 3
Meaning
An exothermic process is one that gives out energy. This usually causes surroundings to increase in temperature.
About Exothermic Processes
- Most chemical reactions are exothermic with means they release energy to the environment and this is observed by an increase in temperature.
 |
| The energy stored in the reactants is released in the chemical reaction making the material increase in temperature. The products now have less energy than the reactants. |
- Freezing, Condensing and Depositing are exothermic changes because they release energy when they happen. The material has less after they have happened. However, there is usually no increase in temperature because the material is usually cooled to change state.
Key Stage 4
Meaning
An exothermic process is one that gives out energy. This usually causes surroundings to increase in temperature.
About Exothermic Processes
Foundation
- Exothermic reactions usually require energy to begin. This is called the activation energy.
- In an exothermic process the potential energy stored in the products is less than the potential energy stored in the reactants.
 |
| To start the reaction an activation energy is needed. This is usually achieved by initially heating the reactants. Once the reaction starts the energy stored in the reactants is released in the chemical reaction making the material increase in temperature. The products now have less energy than the reactants. |
Higher
- In a chemical reaction energy is needed to break the chemical bonds holding the atoms together.
- In an exothermic reaction energy is them released as atoms form new chemical bonds.
- This happens because there is less energy stored in the chemical bonds of the products than the reactants.
Examples
Higher
| Bond | Energy in kJ/mol |
| C-H | 413 |
| O=O | 498 |
| O-H | 464 |
| C=O | 799 |