Energy transfers in reactions Flashcards
(23 cards)
Where is energy transferred to in exothermic reactions?
To the surroundings (EXit - Going out)
What happens in ‘chemical energy —–> thermal energy’?
Thermal energy is released to the surroundings
What happens in ‘thermal energy —–> chemical energy’?
Thermal energy is taken in from the surroundings
What happens to the temperature in exothermic reactions?
It increases
Examples of exothermic reactions?
Combustion reactions, neutralisation reactions, reactions of acids with metals, hand warmers
Where is energy transferred to in endothermic reactions?
From the surroundings (ENtrance - Going in)
What happens to the temperature in endothermic reactions?
Can decrease or may need heat to be added for the reaction to proceed
Examples of endothermic reactions?
Thermal decomposition reaction, photosynthesis, cooling packs
What is activation energy?
The amount of energy needed to start a reaction
What does activation energy make the particles in the reaction do?
Collide with each other so they can react
In exothermic reactions, the product of the reaction have a ___________ energy level than the reactants
Lower
Which reaction has a positive energy transferred number and which one has a negative number?
Exothermic - Negative
Endothermic - Positive
In endothermic reactions, the product of the reaction have a ___________ energy level than the reactants
Higher
What is energy transferred measured in?
kJ/mol
How to work out overall energy change?
Products energy - reactants energy
How to work out total energy change in a reaction?
Energy taken in when bonds are broken - Energy given out when new bonds are formed
What is bond energy?
The amount of energy required to make or break a bond
Negative result = _____
Exothermic reaction
Positive result = _____
Endothermic reaction
What is a cell?
A single power cell, two different metals in contact through an electrode, contains chemicals which react to produce electricity
What is a battery?
Two or more cells connected in series, produce a higher voltage than a cell
Pros of fuel cells (hydrogen)?
Only product is water, continuous supply of energy if the fuel doesn’t run out, very efficient and little energy is wasted as heat
Cons of fuel cells (hydrogen)?
Hydrogen is extremely flammable, hydrogen might be produced using fossil fuels or in a reaction that produces co2, very expensive to make, hydrogen needs to be stored in pressurised containers which could easily explode
