Energy Changes (seneca) Flashcards
in endothermic reactions, energy from the —— is transferred to the ——-, causing the temperature of the surroundings to …
surroundings
reacting chemicals
decrease
what are some examples of endothermic reactions
-thermal decomposition
- The melting of ice to form water.
-Evaporation of liquid water, forming water vapour.
-The baking of bread.
-sports injury packs
-Citric acid + baking soda
in exothermic reactions, energy from the——– is transferred to the ———-, which often —— the temperature as a result
reacting chemicals
surroundings
increases
what are examples of exothermic reactions
Combustion.
Neutralisation.
Oxidation.
handwarmers
Particles of the reactants have to …
collide.
The collisions that happen between particles of the reactants must take place with ———.
This threshold amount of energy is called the…
enough energy.
activation energy.
Reaction profiles show the 1. on the x-axis and 2. on the y-axis.
1.progress of reaction
2.energy level
Reaction profiles tell us:
-The amount of energy contained within the reactants and the products.
-The activation energy of a reaction.
-The overall energy change that happens as a result of a reaction.
What information is contained within reaction profile diagrams?
-The amount of energy contained within the reactants and the products
-The activation energy
-Overall energy change
Catalysts can 1 reaction rates by 2, which …
1.increase
2.lowering the activation energy
3.increases the likelihood of successful collisions.
collisions must have
sufficient energy
in endothermic reactions, Energy released by making bonds – energy required to break bonds
<
in endothermic reactions, overall energy change of reaction >
0
in exothermic reactions, Energy released by making bonds – energy required to break bonds.
>
in exothermic reactions, overall energy change of reaction <
0
Bond making releases 1. It is an 2 process.
1.heat energy
2.exothermic
Bond breaking needs 1. It is an 2. process.
- heat energy
2.endothermic
A reaction is endothermic if…
the total energy released by forming bonds is less than total energy required to break bonds.
what is a catalyst?
A substance that increases the reaction rate by decreasing activation energy
By subtracting the 1. from the 2. , we can see if a reaction is endothermic or exothermic.
1.total bond energies of products
2.total bond energies of reactants
A reaction is exothermic if …
the total energy released by forming bonds is more than total energy required to break bonds.
Batteries and cells contain …
chemicals that react to produce electricity.
We can make a simple cell by …
connecting 2 different electrodes and putting them in a liquid electrolyte.
In a chemical cell, the difference in the reactivity of the metals produces …
a voltage (electricity).
A chemical cell produces ——- until …
a potential difference
the reactants are used up.
How would you describe a cell made by connecting 2 different electrodes and submerging them in an electrolyte?
simple cell
The voltage output of a cell can be changed by …
changing the type of electrode, the type of electrolyte or both the type of electrode and the type of electrolyte.
Changing the electrolyte changes——-. This will result in the…
- the reactions that happen at the electrodes
- voltage output of the cell changing.
A 1. difference in reactivity between 2. will result in the 3…
1.greater
2.the two electrodes
3.cell having a greater voltage.
how would you change voltage output of a (chemical) cell
Type of electrode
Type of electrolyte
In a chemical cell, decreasing the difference in reactivity between the 2 electrodes will ——- the voltage output
decrease
In a chemical cell, electrodes must 1, so 2.
1.conduct electricity
2.metals are often chosen
In a chemical cell, electrolyte contains …
the ions that react with the electrodes.
Chemical cells contain chemicals that react to produce …
electricity
A battery is a collection of …
more than one cell joined in series (end-to-end).
The voltage of a battery is calculated as …
the sum of the voltages of its individual cell components.
When the chemicals in a battery run out, …
the battery can not be used anymore.
voltage of a battery=
Σ(sum of) voltages of individual cell components
Cells and batteries can be either …
rechargeable or non-rechargeable.
In non-rechargeable cells and batteries (e.g. 1.), 2. reactions take place at the …
1.alkaline batteries
2.irreversible
3.electrodes
In non-rechargeable cells and batteries, electricity can no longer be produced …
as soon as one of the reacting chemicals has run out.
In rechargeable cells and batteries, connection to an electric current …
reverses the reactions that happen at the electrodes
In rechargeable cells and batteries, electricity can continue to be produced as long as …
there is access to this external electric current.
What category do alkaline batteries come under?
non-rechargeable
what types of battery?
Connection to an electric current reverses the reactions that happen at the electrodes. This means that electricity can continue to be produced.
Rechargeable
what types of battery?
Irreversible reactions take place at the electrodes. This means that electricity can no longer be produced as soon as one of the reacting chemicals has run out.
Non-rechargeable
In a battery, if more cells are added in series (joined end-to-end), the voltage output of the battery will …
increase
reactions at electrodes are
irreversible
Fuel cells produce 1. using a reaction between 2. and 3
- electrical energy
- an external fuel source (often hydrogen)
- oxygen
The fuel is added to the cell and then there is a…
constant supply of oxygen
In fuel cells, The fuel is ——- and this creates a voltage.
oxidised
In fuel cells, The fuel is oxidised and this creates a …
voltage
what are the advantages of fuel cells ?
-Compact and lightweight
-Reliable
-Less pollution than traditional methods
-High efficiency
why are fuel cells reliable?
The absence of moving parts means they are reliable.
Fuels cells produce electrical energy efficiently by…
using energy produced by a particular reaction
In hydrogen fuel cells, the ——–
of hydrogen generates a voltage and the only waste product is water.
oxidation
In hydrogen fuel cells, the oxidation of hydrogen generates …
a voltage and the only waste product is water.
what is the Hydrogen Fuel Cell anode half equation?
2H2 → 4H+ + 4e-
what is the Hydrogen Fuel Cell cathode half-equation ?
O2 + 4H+ + 4e- → 2H2O
what is the Hydrogen Fuel Cell cathode overall equation ?
2H2 + O2 → 2H2O
ANODE HALF EQUATION -Hydrogen is pumped in at the —–. Hydrogen ions are formed as hydrogen molecules are oxidised and lose electrons.
anode
ANODE HALF EQUATION -Hydrogen is pumped in at the anode. Hydrogen ions are formed as …
hydrogen molecules are oxidised and lose electrons.
ANODE HALF EQUATION -Hydrogen is pumped in at the anode. ——– are formed as hydrogen molecules are oxidised and lose electrons.
Hydrogen ions
CATHODE HALF EQUATION- Oxygen is pumped in at the ——. Water is formed as the O2 reacts with the H+ ions that have moved through the electrolyte from the anode.
cathode
CATHODE HALF EQUATION- —— is pumped in at the cathode. Water is formed as the O2 reacts with the H+ ions that have moved through the electrolyte from the anode.
Oxygen
CATHODE HALF EQUATION- Oxygen is pumped in at the cathode. Water is formed as the 1. reacts with the 2. that have moved through the electrolyte from the anode.
1.O2
2.H+ ions
CATHODE HALF EQUATION- Oxygen is pumped in at the cathode. ——- is formed as the O2 reacts with the H+ ions that have moved through the electrolyte from the anode.
Water
CATHODE HALF EQUATION - Oxygen is pumped in at the cathode. Water is formed as the O2 reacts with the H+ ions that have moved through …
the electrolyte from the anode.
Which reactant is added to which electrode in hydrogen fuel cells?
-Oxygen is added to the cathode
-Hydrogen is added to the anode
Hydrogen fuel cells can be used as alternatives to …
rechargeable batteries (and cells).
hydrogen fuel cells may be better than rechargeable batteries and cells because:
-Toxicity
-Lifetime
-Capacity
What are the risks of hydrogen fuel cells?
Hydrogen has to be stored at a high pressure and hydrogen gas is explosive.
Batteries are made from …
toxic metal compounds and their disposal can cause pollution.
Hydrogen fuel cells use ———– and the only waste product is …
hydrogen and oxygen
water
Batteries must be replaced after …
a certain number of recharges.
Hydrogen fuel cells can be reused indefinitely by …
adding more hydrogen and oxygen.
Hydrogen fuel cells produce more energy per gram of…
hydrogen relative to petrol.
Batteries have a —— capacity than hydrogen fuel cells, and so …
smaller
have to be charged more regularly.
what are the advantages of hydrogen fuel cells?
-high capacity
-low toxicity
-long lifetime
What is formed at the cathode in a hydrogen fuel cell?
water
What are the reactants in fuel cells?
-An external fuel source
-Oxygen
What is represented by the arrow going upwards in the reaction profile?
Activation energy
in a reaction profile the shows to ‘leaps’ which ‘leap’ in the catalysed reaction?
the smaller ‘leap’
How does a catalyst speed up the rate of reaction?
by lowering the activation energy
Endothermic reactions —– energy from the surroundings
absorb
Exothermic reactions —– energy into the surroundings
release
The change in temperature =
final temperature - initial temperature
Energy change (J) =
Volume of solution (cm3) x 4.2 x Change in temperature (C)
Activation energy is the minimum amount of energy needed for particles to…
react.
What does the bottom arrow represent in reaction graphs?
energy change
what would be a suitable solution to act as a electrolyte
All soluble ionic compounds are strong electrolytes
Some polar covalent compounds are also strong electrolytes
What’s the ionic equation that represents the reaction happening at the chromium electrode in the cathode cell?
Cr → Cr3+ + 3e−
