energy changes- c7

Question 1

What happens to energy in chemical reactions?

Answer 1

Energy is transferred during a chemical reaction. So the total energy remains the same before and after a reaction. So energy cannot be created or destroyed, energy is conserved.

Question 2

What is an exothermic reaction?

Answer 2

An exothermic reaction is one that transfers energy to the surroundings, so the temperature of the surrounding increases. This is shown by a rise in temperature.

Question 3

In an exothermic reaction, do the products or reactants have more energy?

Answer 3

The products must have less energy than the reactants.

Question 4

What are examples of exothermic reactions?

Answer 4

Burning fuels(combustion), neutralization reactions and oxidation reactions.

Question 5

What are the everyday uses of exothermic reactions?

Answer 5

• Some hand warmers use exothermic oxidation of iron in the air( with a salt solution catalyst) to release energy.
• Self heating cans of hot chocolate and coffee also rely on exothermic reactions between chemicals and their bases.

Question 6

What is an endothermic reaction?

Answer 6

An endothermic reaction is one which takes in energy from the surroundings. This is shown by a fall in temperature.

Question 7

In an endothermic reaction, do the products have more energy or the reactants?

Answer 7

Products have more energy than reactants

Question 8

What are examples of endothermic reactions?

Answer 8

• reaction between citric acid and sodium hydrogencarbonate.
• thermal decomposition

Question 9

What are the everyday uses of endothermic reactions?

Answer 9

-used in some sports injury packs

Question 10

Exo and endo required practicle info( just read ig)

Answer 10

• You can measure the amount of energy released by a chemical reaction( in solution) by taking the temperature of the reagents( making sure they are the same), mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction.
• The biggest problem with energy measurements is the amount of energy lost to the surroundings
• You can reduce it by putting the polystyrene cup into a beaker of cotton wool to give more insulation, and putting a lid on the cup to reduce energy lost by evaporation.
• This method works for neutralisation reactions or reactions between metals and acids, or carbonates and acids.
• You can also use this method to investigate what effect different variables have on the amount of energy transferred- e.g the mass or concentration of the reactants used.

Question 11

Method for testing the effect of acid concentration on the energy released in a neutralization reaction between hydrochloride acid and sodium hydroxide.

Answer 11

• Put 25cm cubed of 0.25mol/dm cubed of hydrochloric acid and sodium hydroxide in seperate beakers.
• Place the beakers in a water bath set to 25C until they are both at the same temperature( 25)
• Add the HCL followed by NaOH to a polysterene cup with a lid.
• Take the temperature of the mixture every 30 seconds and record the highest temperature
• Repeat steps 1-4 using 0.5mol/dm cubed and then 1mol/dm cubed of hydrochloric acid.

Question 12

What happens in a chemical reaction to bonds?

Answer 12

During a chemical reaction, old bonds are broken and new bonds are formed.

Question 13

Is bond breaking exo or endo?

Answer 13

Endothermic

Question 14

is bond making exo or endo?

Answer 14

Exothermic

Question 15

Why is bond breaking endothermic?

Answer 15

Energy must be supplied to break existing bonds- so bond breaking is an endothermic process.
-In endothermic reactions the energy used to break bonds is greater than the energy released by forming them.

Question 16

Why is bond making exothermic?

Answer 16

Energy is released when new bonds are formed- so bond formation is exothermic.
-In exothermic reactions the energy released by forming bonds is greater than the energy used to break them.

Question 17

What are reaction profiles?

Answer 17

-Reaction profiles are diagrams that show the relative energies of the reactants and products in a reaction, and how the energy changes over the course of the reaction,

Question 18

What is activation energy?

Answer 18

The minimum amount of energy that particles must have to react.

Question 19

What is an electrochemical cell?

Answer 19

An electrochemical cell is a basic system made up of two different electrodes in contact with an electrolyte.

Question 20

info about the electrochemical cell

Answer 20

• The two electrodes must be able to conduct electricity and so are usually metals.
• the electrolyte is a liquid that contains ions which react with the electrodes
• the chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes
• If the electrodes are then connected by a wire, the charge is able to flow and electricity is produced.
• A voltmeter can also be connected to the circuit to measure the voltage of the cell.