Energy Changes

Question 1

Exothermic reaction

Answer 1

Heat is given out, this shown in a temperature rise

The best example of exothermic reaction is burning fuels - also called combustion.

Question 2

Endothermic reaction

Answer 2

Heat is taken. Shown in a fall in temperature.
Examples of this could be thermal decomposition
Or reaction between citric acid and sodium hydrogencarbonate

Question 3

How to measure energy transferred by a chemical reaction?

Answer 3

By taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction

Question 4

Method for energy transferred practical

Answer 4

1) put 25cm^3 of 0.25 mol/dm^3 of hydrochloric acid and sodium hydroxide in separate beakers.
2) place the beakers in a water bath set to 25 degrees until they are both at the same temperature .
3) add the HCl followed by the NaOH to a polystyrene cup with a lid.
4) take the temperature of the mixture every 30 seconds, and record the highest temperature.
5) repeat steps 1-4 using 0.5mol/dm^3 and then 1 mol/dm^3 of hydrochloric acid

Question 5

What is a reaction profile

Answer 5

Shows energy changes

Question 6

Bond energies

Answer 6

Energy must always be supplied to break existing bonds - endothermic
Energy is released when new bonds are formed - exothermic

Question 7

Chemical reactions in a cel produce

Answer 7

Electricity

Question 8

The voltage of a cell depends on many factors. Name the factors

Answer 8

Different metals

Type of electrode

Question 9

In non rechargeable batteries what happens?

Answer 9

Reactants get used up and turned into the products of the reaction. Once any one of the reactants is used up, the reaction can’t happen and so electricity is produced. The products can’t be turned back into the reactants, so the cell cant be recharged.

Question 10

Fuel cells

Answer 10

Use fuel and oxygen to produce electrical energy

Question 11

Hydrogen-oxygen fuel cells

Answer 11

Involves a redox reaction.
At the negative electrode (anode), hydrogen loses electrons to produce H+ ions. This is oxidation.

At the positive electrode (cathode), oxygen gains electrons from the cathode and reacts with H+ ions to make water. This is reduction

Question 12

Uses of Hydrogen-oxygen fuel cells

Answer 12

Could be used in vehicles because:
It does not produce as many pollutants as other fuels
Only by products are water and heat
Batteries are more expensive to make then fuel cells
Batteries also store less energy, so they must be recharged a-lot more often