C7- Energy Change Flashcards
1) What does ‘energy is conserved in chemical reactions’ mean? (2 marks)
The amount of energy in the universe at the end if the chemical reaction is the same as before the chemical reaction.
2) How much energy do the product molecules have if energy is transferred to the surroundings? (1 mark)
Less energy that the reactants
3) What is an exothermic reaction? (2 marks)
A reaction that transfers energy to the surroundings so the temperature of the surroundings increases
4) What are some examples of exothermic reactions (3 mark)
Combustion reactions, many oxidation reactions and neutralisation reactions
5) What is an endothermic reaction? (2 marks)
A reaction that takes in energy from the surroundings so the temperature of the surroundings decreases
6) What are some examples of endothermic reactions? (2 marks)
Thermal decomposition, and the reaction of citric acid and sodium hydrogen carbonate
7) What type of reaction is it if the temperature of the surroundings goes down? (1 mark)
Endothermic
8) What are some everyday uses of endothermic reactions? (1 mark)
Sports injury packs (like ice packs)
9) What type of reaction is it if the temperature of the surroundings goes up? (1 mark)
Exothermic
10) What are some uses of exothermic reactions? (1 mark)
Hand warmers, self-heating cans
11) When can a chemical reaction occur? (2 marks)
Only when reacting particles collide with each other and with sufficient energy
12) What is the name of the minimum amount of energy required to start a chemical reaction? (1 mark)
Activation energy
13) What is a reaction profile? 3 marks)
• It is a diagram that shows: • Relative energies of the reactants and products • Activation energy • Overall energy change of a reaction
14) What does the reaction profile for an exothermic reaction look like? (3 marks)
15) What does the reaction profile for an endothermic reaction look like? (3 marks)
16) How can you calculate the energy absorbed or released during a chemical reaction?
• Energy must be supplied to break bonds in the reactants • Energy is released when bonds are formed in the products • Sum of energy required to break the bonds - Sum of energy released making new bonds
16) How can you tell if the reaction is exothermic? (2 marks)
The overall energy change will be NEGATIVE as the amount of energy released is greater than the energy required to break the bonds.
17) How can you tell if the reaction is endothermic? (2 marks)
The overall energy change will be POSITIVE as the amount of energy required to break the bonds in the reactants is greater than the energy released in forming the products
18) What is a cell? (2 marks)
Cells contain chemicals which react to produce electricity
19) What is the voltage of a cell dependent upon? (2 marks)
• The type of electrode • The electrolyte
20) How can you make a basic cell? (2 marks)
By connecting two different metals in contact with an electrolyte
21) What is a battery? (2 marks)
Two or more cells connected together to provide greater voltage
22) What happens in non-rechargeable cells? (1 mark)
• The reactions stop when one of the chemicals is used up • Alkaline batteries are non-rechargeable
23) How are rechargeable cells able to be recharged? (1 mark)
The chemical reactions are reversed when an external electrical current is supplied
24) How does the difference in reactivity between affect the voltage of the cell? (1 mark)
The greater the difference in reactivity, the greater the voltage
25) What is an example of external fuel for a fuel cell? (1 mark)
Hydrogen and Oxygen (or air)
26) What happens to the fuel in order to produce a potential difference? (2 marks)
The fuel is oxidised electrochemically
27) What is the overall reaction in a hydrogen fuel cell? (2 marks)
Hydrogen is oxidised to produce water (no pollution/carbon dioxide) PIC
