5 Energy changes Flashcards
1
Q
what is an exothermic reaction
A
- transfers energy to its surroundings - rise in temp of surroundings
- eg. combustion
2
Q
what is an endothermic reaction
A
- takes in energy from its surroundings
- fall in temp of surrounding
3
Q
practical measuring energy transfer
A
4
Q
exothermic reaction profile
A
- energy on x
- progress of reaction on y
- reactants at the top
- products on the bottom
- activation energy from reactants to peak
- energy released from reactants to products
5
Q
endothermic reaction profile
A
- energy on x
- progress on y
- reactants in bottom
- products at top
- activation energy from reactants to peak
- energy change from reactants to absorbed
6
Q
what is activation energy
A
- minimum amount of energy that reactants need to collide with each other and react
- greater the activation energy the more energy needed to start the reaction
- catalysts provide an alternative reaction pathway with a lower activation energy
7
Q
in which reaction do bonds break
A
- endothermic
- energy must be supplied to break existing bonds
8
Q
in which reaction do bonds form
A
- exothermic
- energy released when new bonds are formed
9
Q
how to calculate overall energy change
A
sum of energy released when breaking bonds - energy released when forming
10
Q
how to produce an electrochemical cell
A
- in a beaker put an electrolyte eg. NaCl
- must have 2 electrodes which are able to conduct electricity
- both are connected with wire
11
Q
how does a cell work
A
- chemical reactions between the electrodes set a charge difference between the electrodes
- elctrodes are connected with wire which alows the charge to flow and electricity is produced
- voltmeter can be connected to measure the voltage of the cell
12
Q
what does the voltage fo a cell depend on
A
- type of electrode used - different metals react differently
- the bigger the difference in reactivity the bigger the voltage
- the electrolyte used - different ions in solution will react differently with the metal
- wether there are multiple cells connected - battery, in battery voltage will be bigger overall
13
Q
how do non-rechargable batteries work
A
- chemical reactions that happens at thelectrodes are irreversible
- overtime the reactant particle -ions in electrolyte, metal ions in electrode get used up and turn into products of reaction
- one a reactant in used up a reaction can’t happen so no electricity is produced
- products can’t be turned back into reactants so cell can’t be reacharge
- however in rechargeable reaction can be reversed by connecting it to an external electric current
14
Q
in fuel cells which one is the cathode and anode
A
- cathode - positive
- anode - negative
15
Q
how do fuel cells work
A
- electrolyte is often a solution of potassium hydroxide
- eletrodes are porous carbon with a catalyst
- hydrogen goes into the anode compartment and oxygen goes into the cathode compartment
- at the -ve elctrode anode hydrogen looses electrons to produce H+ ions -oxidation
- H+ ions move to the cathode +ve
- at the +ve elctrode, oxygen gains electrons form he cathode and react with H+ ions to make water - reduction
- electrons flow though an external circuit from the anode to the cathode - produces electric current
- overall reation is hydrogen plus oxygen
