(Topic 5) Energy Changes (CGP Book) Flashcards
What happens to energy in a reaction?
It is conserved, meaning it can not be created or destroyed, only moved around.
What happens in an exothermic reaction?
Heat is given out meaning energy transferred to surroundings
Examples of exothermic reaction?
- combustion
- neutralisation reactions
- oxidation reactions
- hand warmers
What is an endothermic reaction?
Takes in energy from surroundings
Examples of endothermic reaction?
- citric acid and sodium hydrogencarbonate
- Thermal decomposition
- Sports injury packs
Describe the graph of an exothermic reaction?
- products at lower energy than all reactants
- difference in height represents overall energy change in reaction
- initial rise in energy represents energy needed to start reaction (known as activation energy)
What is activation energy?
Minimum amount of energy the reactants need to collide with each other and react. The greater the activation energy, the more energy needed to start the reaction
Describe the graph of an endothermic reaction?
- products at higher energy than reactants
- difference in height represents the overall energy change during the reaction
What happens during a chemical reaction?
- Old bonds broken and new ones made
- energy must be supplied to break existing bonds - endothermic
- energy released when new bonds formed - exothermic
What happens in a chemical reaction in a cell?
electricity produced
Describe how a chemical reaction in a cell works?
- Two electrodes able to conduct electricity (usually metals)
- The electrolyte is a liquid that contains ions that react with the electrodes
- chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes.
- if electrodes connected with wire then charge is able to flow and electricity is produced. A voltmeter can be used to measure voltage
What happens if their is a big difference in electrode reactivity?
Bigger the voltage in the cell
What happens in non-rechargeable batteries?
- chemical reactions at electrode are irreversible
- ions in electrolyte and metal ions in electrode get used up and turned into products
- once one reactant used up, reaction can’t happen and no electricity produced
- products can’t be turned back into reactants, so cell can’t be recharged
What is a fuel cell?
An electrical cell that is supplied with fuel and oxygen and uses energy from reaction between them to produce electrical energy efficiently
What happens in a fuel cell?
When fuel enters cell, it becomes oxidised and sets up a potential difference in the cell
