Energy in bonds, fuels and graphs Flashcards
Changes in energy during reactions can be explained by the …..?
making or breaking of bonds
What is an exothermic reaction?
e.g
One that gives out energy to the surroundings usually in the form of heat and is usually shown as a rise in temperature.
combustion of fuels
What is an endothermic reaction?
e.g
One that takes in energy from the surroundings usually in the form of heat and is usually shown as a fall in temperature.
photosynthesis
Energy must always be supplied to …
It must always be released for …
break bonds
bonds to form
What happens during a chemical reaction to bonds?
old bonds are broken and new bonds are formed
Why is bond breaking an endothermic process?
As energy must be supplied to break the existing bonds, energy taken from the outside
Why is bond formation an exothermic process?
As energy is released when new bonds are formed
In an endothermic reaction the … required to …. old bonds is … than the energy …. when new … are formed.
energy, break, more, released, bonds
In an exothermic reaction the … released in bond … is … than the energy used in … old bonds.
energy, formation, more, breaking
How can you measure energy released by a chemical reaction?
What is the problem with this?
How can you make this better?
What does this method work for? Reactions of (2):
By taking the temp of the reactants (both must be the same) mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction.
Energy is lost to surroundings which is not shown in the results.
Reduce the radiation by putting the polystyrene cup unto a beaker of cotton wool to give more insulation and putting a lid on it to prevent evaporation
solids with water, neutralization reactions
What is an example of a reaction where energy released is measured? (4)
What else could this method be used for?
Place dilute HCl in a polystyrene cup and record the temp
Put dilute sodium hydroxide in a measuring cylinder and record temp’
As long as they’re at the same temp add the alkali and stir into the acid
Take the temp every 30 secs and record the highest temp it reaches
When energy is absorbed, there will be a fall in temp
Fuels release…
burning fuels affects ….. . For example burning fossil fuels…. causing…..
energy
the environment
releases the greenhouse gas CO2, global warming and other types of climate change
Why is it expensive to use fossil fuels?
It’s expensive to slow down the negative effects and and to put things right, as well as developing alternative solutions
What’s running out that our fuels are made from?
So as they … …. they will get …. …..
So everything …. by … , …. , or ….gets more … too. So the price of … … has a large … effect.
Fossil fuels
run out, more expensive
transported, lorry, train, plane, expensive. crude oil, economic
What is calorimetry?
When you try to find out how much energy released when a fuel is burnt by burning the fuel to heat water and measuring the temperature change.
What is the calorimetry method?(5)
- Put a measured amount of water in the copper can and record its temperature.
- Weigh the spirit burner and lid.
- Put the burner under the can and light the wick. Stir the water and until the temp reaches 50 degrees.
- put out the flame using the burner lid and measure the final temp of water.
- Weigh the spirit burner.
What is the formula to find out the energy transferred in the calorimetry test?
Energy transferred (Joules) = mass of water (in g) x specific heat capacity (=4.2) x temperature change (Δ)(in degrees)
What do energy level diagrams show?
If an experiment is endo or exothermic
In exothermic reactions, what type of energy change is there?
ΔH (energy change) is negative
the energy in the reactants goes down, it’s released.
The energy level diagram is for an exothermic reaction.
Describe its shape… 1. axes 2. starting height, middle, finishing height, 3. ΔH is what? 4.What are the horiz labeled as?
X is progress of reaction, y energy
horizontal flat line going right, a bump of energy needed to break the old bonds, the activation energy, then it falls down lower than the original line and flattens out.
-ve
reactants, products
In an exothermic reaction diagram the lines are at different heights, which are where?
What does the difference in height represent?
What are the energy transfers in the two types of diagram (positive or negative?)
The products are lower than the reactants
The energy given out in the reaction per mole.
Exo = ΔH -ve, Endo = ΔH+ve
The energy level diagram is for an endothermic reaction.
Describe its shape… 1. axes 2. starting height, middle, finishing height, 3. ΔH is what? 4.What are the horiz labeled as?
X is progress of reaction, y energy
horizontal flat line going right low on the diagram, the line rises high, then fall a bit, then flattens out onto the horizontal.
3. +ve,
4. reactants, products
The energy level diagram is for an endothermic reaction.
5. What does the difference in height represent? 6. What is the activation energy? 7. What is the energy absorbed?
- The energy taken in during the reaction. 6. From the first horizontal to the top of the peak. The distance between the first horizontal and the second.
What does the activation reaction represent?
What does a catalyst do?
What is this represented by on the energy level diagrams?
But what stays the same?
The minimum energy needed by reacting particles to break their bonds.
Provides a different pathway for a reaction that has a lower activation energy so it happens more quickly and easily.
A lower curve on the diagram showing a lower AEnergy
The overall energy change in the reaction ΔH
