P1. Topic 5 Energy Changes 🥈 Flashcards
Outline some basics of energy
Can’t be created nor destroyed and can only be transferred
What is Chemical energy
Energy stored in the bonds between atoms.
SI unit for energy
Joules
What are the Energy changes during a chemical reaction
Energy is released or absorbed during a chemical reaction depending on the relative energies of the bonds within the reactants and products.
Describe an Exothermic reaction and reaction profile
If the total chemical energy of the products is lower than the total energy of the reactants, energy will be released from the system into the surroundings.
Give an Example of an exothermic reaction
Combustion of methane and respiration.
Describe an Endothermic reaction and reaction profile
If the total chemical energy of the products is higher than the total energy of the reactants, energy will be absorbed from the surroundings.
Give an Example of endothermic reaction
Decomposition of water by electrolysis and photosynthesis
What happens to heat in an exothermic reaction
It is given out
What happens to heat in an endothermic reaction
It is taken in
List the equipment you need to measure energy transfer in a practical and state the purpose of them
Polystyrene cup- insulates, doesn’t allow heat to enter or escape
Thermometer- measure temperature (then calculate temperature change)
Lid- prevents heat entering or escaping
Beaker- provides stability for the polystyrene cup
Measuring cylinder- allow the same volume of acid to be used each time
State the variables in the energy transfer practical
Independent- concentration of acid
Dependant- temperature change
Control- volume of acid and initial temperature as well as mass of metal
What does temperature increase indicate
The reaction is exothermic
What does temperature decrease indicate
The reaction is endothermic
Describe the energy changes (exothermic/endothermic) practical (6)
Place the polystyrene cup inside the glass beaker to make it more stable.
Measure an appropriate volume of the solution, eg 25 cm3.
Measure an appropriate mass of the solid, or select a suitable sized piece of metal.
Place the solution in a polystyrene cup.
Record the initial temperature of the solution.
Add the solid and record the highest or lowest temperature obtained.
Calculate the temperature change by doing final final temperature - initial temperature
What do reaction profiles show?
Energy changes
Is this reaction profile endothermic or exothermic and why
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Exothermic, products are below reactants
Is this reaction profile endothermic or exothermic and why
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Endothermic, products are higher than reactants
What is labelled x
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Energy
What is labelled x
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x
Progress of reaction
What is labelled x
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Reactants
What is labelled x
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Products
What is labelled x
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Activation energy
What is labelled x
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Overall energy change
