Heat Energy Changes in Chemical Reactions

Question 1

Which solution contains the greatest number of ions?

Answer 1

B - iron lll chloride

Question 2

Devise a plan to compare the temperature changes produced when sodium hydroxide solution is neutralised with each of the these two acids

Answer 2

• measure know volume of sodium hydroxide solution
• add same volume of each of the acids
• stir the mixture
• record initial and final temperatures (temp change)

Question 3

Explain what the temperature readings show about the type f heat change occurring when ammonium chloride dissolved in the water

Answer 3

• temperature decreases (heat energy taken in)

- so endothermic

Question 4

Which row of the table shows the heat energy changes that occur when bonds are broken or formed

Answer 4

D - bonds broken = heat energy required

bonds formed = heat energy is released

Question 5

Explain how the rate of reaction between a solid and liquid is altered by changing the size of the pieces of solid and by changing the temperature of the liquid (6)

Answer 5

smaller pieces of solid:

• large surface area increased
• more frequent collisions
• higher and faster rate of reaction

higher temperature of solids:

• particles move faster because they gain kinetic energy
• more frequent collisions
• particles have more energy
• more collisions have required energy to react
• more successful collisions
• higher rate of reactions

Question 6

Which one of these would decrease the rate of reaction?

Answer 6

A - using hydrochloric acid which is more dilute

Question 7

Explain why increasing the temperature of a reaction increases the rate of reaction

Answer 7

• particles have more energy
• more frequent collisions
• more likely to be successful collisions

Question 8

Explain in terms of the energy involved in the breaking of bonds and in the making of bonds, why some reaction are exothermic.

Answer 8

• energy needed to break bonds
• energy released when bonds formed
• more energy is released than needed

Question 9

Evaluate these results, explain the reasons why rate of reaction is faster than rate of reaction in 2.

Refer to frequency and energy of collisions in your answer

Answer 9

CONCENTRATION:

• experiment 2 had higher concentration of acid
• so more particles in the same volume
• so more frequent collisions between particles
• more successful collisions
• faster rate of reactions

TEMPERATURE:

• experiment 2 had higher temperature
• particles have more energy so move faster
• so more frequent collisions
• higher chance of successful collisions
• more energetic collisions
• so higher rate of reaction as particles have enough energy to react when colliding

mass of both is the same so has no affect on the rate of reaction