C7 - Energy Changes Flashcards
What happens during an exothermic reaction
During exothermic reactions the reacting molecules give off energy to their surroundings
This causes an increase in the temperature of the surroundings
Describe an energy profile diagram for an exothermic reaction
In an energy profile diagram for an exothermic reaction the products have less energy that their surroundings. This is because during the reaction they give off energy to the surroundings
What does the difference between the energy of the reactants and the energy of the products tell
The difference between the energy of the products and the enrgy of the reactants tells us the amount of energy given off to the surroundings during the reaction
What are some examples of products with exothermic reactions
Hand warmers
Self heating cans
What happens during an endothermic reaction
During an endothermic reaction energy is taken in from the surroundings
This causes a decrease in the temperature of the surroundinhs
Describe an energy profile for a endothermic reaction
In an energy profile for an endothermic reaction the products have more energy than the reactants because energy is being taken in from the surroundings
The amount of energy being taken in can be worked out by the difference between the products and the reactants
What is the collision theory
The collision theory states that particles have to collide with sufficient energy in order to react
What is the activation energy and how can it be represented on a graph
The activation energy is the minimum amount of energy needed for particles that collide to react
It is represented on a energy profile diagram by the difference in energy between the reactants and the peak in the curve
How are exothermic reactions represented in terms of energy change
Exothermic reactions are shown as negative energy changes because energy is being transferred to the surroundings
How are endothermic reactions represented in terms of energy changes
Endothermic reactions are represented through a positive energy change.Energy is taken in from the surroundings
What does making bonds do to energy
Making bonds releases energy and so is exothermic
What does breaking bonds do to energy
Breaking bonds requires energy and so is endothermic
What do cells and batteries use to produce electricity and what will eventually happen to the reactants
Cells and batteries use a chemical reaction to produce electricity but eventually the reactants run out
What is the equation for the negative electrode of a hydrogen fuel cell
H^2—->2H+ + 2e-
The hydrogen is split into 4 hydrogen ions and 4 electrons
These electrons run through the wire and provide the electricity
What is the equation for the positive electrode
02 + 4H+ 4e- —-> 2 H20
The hydrogen ions combine with the oxygen to produce water
What is the overall equation for the hydrogen fuel cell
2H+ + O2 —–>H2O
The hydrogen has been oxidised
What are the advantages of a hydrogen fuel cell
- The fuel cell will produce as electricity for as long as you supply hydrogen
- The fuel cell does not become less efficient over time
What are disadvantages of a hydrogen fuel cell
- the hydrogen fuel cell run on hydrogen which is an explosive gas that is hard to store
- Hydrogen fuel cells produce a relativley low amount of potential energy so lots have to be used together
How does a cell produce electricity
When to different metals are placed in an electrolyte they can produced electricity
An electrolyte is a solution which conducts electricity
How long can a cell produce electricity for
A cell can only produce electricity for a certain amount of time before the chemicals in the cell run out and the reaction stops
How does the difference in reactivity affect the electricity produced by the cell
The greater the difference in reactivity between the two metals in the cell , the greater the amount of energy produced .
What does a battery contain
A battery contains two or more cells in a series to produce a greater voltage
What are the advantages of rechargeable batteries
- They require no dangerous gases to run
- They produce a higher potential difference than hydrogen cells
What are disadvantages of rechargeable batteries
- They can store less energy each time they go through a charging cycle and eventually need to be replaced
- They can run out and have to be recharged
What are the disadvantages of non rechargeable batteries
The reactants in non reachargeable batteries get used up and the reaction can no longer take place
The reaction is irrevesable
What is a method you can use for a caliometry experiment
- Use a measuring cylinder to measure 25cm3 of sodium hydroxide solution
- Put a polystyrene cup in the 250cm3 beaker
- Use another measuring cylinder to measure 25cm3 of hydrochloric acid
- Add the sodium hydroxide solution to the polystyrene cup. Use a thermometer to measure the temperature of the sodium hydroxide solution every thirty seconds whilst gently stirring it
- After exactly 2 minutes add the hydrochloric acid to the solution, and now measure the temperature of the solution every 30 seconds for 10 minutes
- Measure the temperature change in the solution and decide from this wether the reaction is endo or exo thermic ( Endo if the temperature goes up , exo if it goes down )
