Unit 7 Energy Changes Flashcards
What’s an exothermic reaction
A reaction that transfers energy from reacting molecules to the surrounding
Name a common example of an exothermic reaction
Wood burning
What’s an endothermic reaction
A reaction that takes in energy from the surroundings
What happens to the surroundings during an exothermic reaction
The temperature of the surroundings increases
What is combustion
Burning
Is oxidation an endo or exothermic reaction
Exothermic
Is neutralisation an endo or exothermic reaction
Exothermic
What is and energy profile
A graph with the time of reaction on the x axis and energy changes on the y axis
On the energy profile for exothermic reactions is the energy of the reactants higher that the products
The energy of the reactants is above the energy of the products
What does the difference in the levels of energy of the reactants and products in a energy profile show
The total energy released to the surroundings
On the energy profile of an **endothermic reaction ** is the energy of the reactants higher than the energy of the products
No
The energy of the products is higher than the energy of the reactants
Name the two uses for exothermic reactions
Hand warmers
Self heating objects
What is a common example of an endothermic reaction
Thermal decomposition
Is thermal decomposition endo or exothermic
Endothermic
What happens to the surroundings during a endothermic reaction
The temperature of the surroundings decreases
What is the activation energy
The minimum amount of energy need for the reaction to occur
Why is there an activation energy
Because there is a minimum amount of energy to make the particles collide
How do you identify the activation energy on an energy profile
From the reactants to the peak of the curve
Which requires more energy to occur endo or exothermic reactions
Endothermic reactions
Are energy changes for exothermic reactions + or -
Negative
Why are exothermic reactions energy changes negative
Because energy is being transferred (lost) to the surroundings
Are endothermic reactions energy changes + or -
Positive
Why are endothermic reactions energy changes positive
Because energy is gained from the surroundings
Is the breaking of bond’s endo or exothermic
Endothermic
Why are breaking bonds endothermic
Because it requires energy to break the bond
Is making bonds endothermic or exothermic
Exothermic
Why is making bond exothermic
Because we release energy when making bonds
Every chemical bond has a what
Energy value
What does the energy value tell us
The energy required to break that bond
H2 + Cl2 ———> 2HCl
Which bond are broken and which are being made
The H an Cl are breaking
The 2HCl is being made
What is the formula for total energy value
Total of bond breaking
———————-————
Total of bong making
What type of reaction is the required practical temperature changes
Neutralisation
What are the steps to the temperature changes practical
-Add increasing volumes of alkali into the acid
-Record the maximum temperature reached
What is the independent variable in the temperature changer RP
The volume of alkaline
What is the dependant variable in the temperature change RP
The maximum temperature reached
What is the control variables in the temperature change RP
The volume of acid and concentration of both the acid and alkaline
Sate the equipment used in the temperature change Rp in order of use
Measuring cylinder
Polystyrene cup
Beaker
Thermometer
Plastic lid
Why do we use a polystyrene cup with a lid in the temperature change RP
To avoid heat escaping to the surroundings and its a good insulator
Why Do we place the polystyrene cup in the beaker
To avoid the polystyrene cup from falling over
What are the acid and alkaline solution used in the temperature change RP
Acid - HCl
Alkaline- NaOH
On the graph of the results on the experiment (temperature change RP) we can see the more Alkaline added the temperature increases
Why
Because when we add more NaOH there are more particles to react with the HCl
On a certain point on the temperature change RP graph the temperature starts to go back down why
Because there is too much NaOH that HCl becomes the limiting reactants do some particles of NaOH don’t react
Explain in terms of energy why at a certain point on the graph of temperature changes RP the temperature decreases
Because the energy released is being spread over a greater volume so each net temperature is lower
What’s an electrolyte
A solution that ions can move through
Describe the strict of a chemical cell
two metals in an electrolyte which produces electricity
Why do cells eventually stop working
Because the chemicals in the cell run out and the reactions stop happening
How do cells create electricity
The metals and the electrolyte react producing an electrical current
Why does two metals with the biggest difference in reactivity produce the most electricity
Because these two metals create the largest potential difference
Why is the best metals to use in a cell magnesium and copper
Because these two metals have the largest difference in reactivity
What other factor others than the two metals used affect the amount of volts produced
The electrolyte
What is a battery is it better than a cell
A battery is an object that contains two or more cells connected in series to produce a greater voltage than cells
Name an example of non rechargeable battery and why is it considered non rechargeable
Alkaline batteries
Because you can’t reverse the reactions
Name an example of a rechargeable battery and why are they rechargeable
Lithium battery’s
Because we can reverse chemical reactions when an electrical current is applied
State the names and charges of the electrodes in the Fuel cell
Anode - negative
Cathode - positive
How does a fuel cell work 1st step
-Hydrogen comes in from one side and reacts with the negative anode to form H plus and negative electrons
What does the wire that’s connected to the two electrodes do
It allows electrons to move from the side to the cathode
How do fuel cells work 2nd step
The electrons move through the wire to the cathode whilst the hydrogen moves through the electrolyte to the cathode
How to fuel cells work 3rd step
Oxygen comes in from the other side and react with the H+ and the - electrons to form water
Why do we need two hydrogen molecules in a fuel cell
Because there will be an oxygen still left to react
State the half equation for Hydrogen in the fuel cell
H2 ———> 2H+ + 2e-
State the half equation for the water produced in a fuel cell
O2 + 4H+ + 4e- ————> 2H2O
State the overall equation in the fuel cell
O2 + 2H2 ———> 2H20
State the advantages of using Hydrogen fuel cells
- They only require H and O
- They don’t produce CO2
- Simple and last longer
State the disadvantages of Hydrogen fuel cells
- Hydrogen gas is hard to store
- Requires energy to use anyway
