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Chemistry > topic 5 - energy changes > Flashcards

topic 5 - energy changes Flashcards

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1
Q

what is the conservation of energy principle?

A
  • energy is conserved in chemical reactions
  • the amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place
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2
Q

what is an exothermic reaction?

A
  • a reaction where energy is transferred to the surroundings so that the surroundings temperature increases
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3
Q

what is an endothermic reaction?

A
  • a reaction where energy is taken in from the surroundings so the surroundings temperature decreases
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4
Q

what is activation energy?

A
  • minimum amount of energy that particles need to react
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5
Q

what is a reaction profile?

A
  • a graph which shows the relative energies of reactants and products, as well as the activation energy of the reaction
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6
Q

what are examples of exothermic reactions?

A
  • combustion
  • certain oxidation reactions
  • neutralisation
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7
Q

what are examples of endothermic reactions?

A
  • thermal decomposition
  • reaction of citric acid
  • sodium hydrogen carbonate
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8
Q

describe exothermic and endothermic reactions in terms of bond energies

A
  • when we break a chemical bond, this requires energy (endothermic)
  • making bonds releases energy (exothermic)
  • this tells us the energy required to break that bond
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9
Q

what are the variables in the temperature changes required practical?

A
  • (independent variable is the volume of sodium hydroxide solution)
  • (dependent variable is the maximum temperature reached)
  • (control variables are the volume of hydrochloric acid, and the concentrations of both the hydrochloric acid and the sodium hydroxide solution)
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10
Q

what are bases?

A
  • bases are chemicals which can neutralise acids and produce salt and water
  • bases which are soluble in water are also called alkalis
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11
Q

what do the most common acids produce?

A

hydrochloric acid -> … chlorides
sulfuric acid -> … sulfates
nitric acid -> … nitrates

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12
Q

describe how to investigate the variables that affect temperature changes in chemical reactions

A
  • use a measuring cylinder to measure 30cm of dilute hydrochloric acid
  • transfer the acid to a polystyrene cup
  • now we stand the polystyrene cup inside a beaker
  • this stops the cup from falling over
  • use a thermometer to measure the temperature of the acid
  • record this in a table
  • use a measuring cylinder to measure 5cm3 of sodium hydroxide solution and transfer this to the polystyrene cup
  • fit a plastic lid to the cup and place the thermometer through the hole in the lid
  • the bulb of the thermometer must be in the solution
  • use the thermometer to gently stir the solution
  • because this reaction is exothermic, it releases energy
  • this means that the temperature of the solution will increase
  • when the reading on the thermometer stops changing, record the highest temperature reached
  • rinse out and dry the polystyrene cup
  • repeat the whole experiment using 10cm3 of sodium hydroxide solution
  • Carry out the experiment several more times + each time we increase the volume of sodium hydroxide by 5cm3 until we reach a maximum of 40cm3 of sodium hydroxide solution
  • repeat the whole experiment one more time so that we have two sets of results
  • use these to calculate a mean value for the maximum temperature reached for each volume of sodium hydroxide solution
  • at the end plot a graph of the results
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13
Q

what is a cell?

A
  • a cell is composed of two electrodes dipped in an electrolyte solution
  • contain chemicals which react to produce electricity
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14
Q

what is an electrolyte?

A
  • a solution that can conduct electricity
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15
Q

what is a battery?

A
  • a battery contains two or more cells connected in series to produce a greater voltage
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16
Q

how long can a cell produce electricity?

A
  • a cell can only produce electricity for a certain period of time
  • eventually, the chemicals in the cell run out and the reaction stops
17
Q

what are the conditions needed for the cell to produce electricity?

A
  • cells can only produce electricity if we use metals with different reactivities
18
Q

what determines the amount of p.d produced by the cell?

A
  • the greater the difference between the reactivity of the metals, the greater the potential difference produced by the cell
  • the electrolyte also affects the potential difference
19
Q

what are the advantages and disadvantages of rechargeable batteries?

A
  • expensive
  • used many times
  • cheap in the long run
  • output stays constant until flat
  • creates less chemical pollution
20
Q

what are the advantages and disadvantages of non-rechargeable batteries?

A
  • cheap
  • only can be used once
  • expensive in the long run
  • output falls gradually
    -creates a lot of chemical pollution
21
Q

what is an electrode?

A
  • a conductor that is used to gain electrical contact with a circuit
22
Q

how can you create a simple cell using electrodes and an electrolyte?

A

connect two different metals and dip them into an electrolyte

23
Q

how do cells generate electricity?

A
  • the more reactive metal gets oxidised
  • the electrons flow through the wire from the more reactive metal to the less reactive metal
  • the rate of flow if electrons is an electric current
24
Q

what are the 4 factors that affect the voltage of a cell?

A
  • the type of electrode used
  • the electrolyte used
  • the concentration of the electrolyte
  • the temperature
25
Q

why can a rechargeable battery be recharged?

A
  • the chemical reactions are reversed using an external electric current
26
Q

what are fuel cells?

A
  • cells that are supplied by an external source of fuel
27
Q

what is the overall reaction in a hydrogen fuel cell?

A

hydrogen + oxygen -> water

28
Q

in a hydrogen fuel cell, where does the oxidation of hydrogen take place?

A

at the anode

29
Q

in a hydrogen fuel cell, what happens at the cathode?

A

the oxygen is reduced

30
Q

give 3 advantages of using hydrogen fuel cells over rechargeable batteries

A
  • do not need to be electrically recharged
  • no pollutants are produced
  • can be a range of sizes for different uses
31
Q

give 3 disadvantages of using hydrogen fuel cells over rechargeable cells and batteries

A
  • hydrogen is highly flammable
  • hydrogen is sometimes produced for the cell by non-renewable sources
  • hydrogen is difficult to store

Chemistry (10 decks)

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