Chemistry chapter 7 (Chemical Energetics)

Question 1

Properties of physical changes

Answer 1

. A change that occurs without changing the identity of the new substance.
. No new substance is created
. Easily reversible

Question 2

Examples of physical changes?

Answer 2

. Change in size, shape or color
. Pencil shavings
. Torn paper
. Crushed ice
. Sugar dissolved in water

Question 3

Properties of chemical changes?

Answer 3

. A change that occurs that causes the identity of a substance to change
. New substances with new properties are formed
. Difficult to reverse
. Energy can be given out (Exothermic) or take in (Endothermic) during the reaction

Question 4

How do we know when a chemical reaction has taken place?

Answer 4

. Colour change
. Participate formation
. Gas formation
. Odour
. Temperature change
. Light production
. Change in acidity

Question 5

Define volatile?

Answer 5

A substance that easily evaporates at normal temperatures.

Question 6

Energy changes in Endothermic reaction?

Answer 6

Breaking chemical bonds takes in energy from the surrounding

Question 7

Energy changes in Exothermic reaction?

Answer 7

Making chemical bonds gives out energy to the surrounding

Question 8

Difference between Exothermic and Endothermic?

Answer 8

Exothermic:
. Bond is stronger in the products
. More energy is released than absorbed
. -ve∆H

Endothermic:
. Bond is stronger in the reactant
. More energy is absorbed than released
. +ve∆H

Question 9

Define heat reaction(∆H)?

Answer 9

Energy change from reactants to products in a chemical reaction, its unit is KJ and is calculated per mole.

Question 10

Which type of reaction takes in heat from its surroundings?

Answer 10

Endothermic

Question 11

Which type of reaction emits heat to its surroundings?

Answer 11

Exothermic

Question 12

Define bond energy?

Answer 12

Average value obtained for a particular bond

Question 13

In what type of reaction is a bond creatred?

Answer 13

Exothermic

Question 14

What type of reaction is a bond broken?

Answer 14

Endothermic

Question 15

How to calculate ( ∆ H)?

Answer 15

The energy needed to break bonds - Energy given out when bonds form

Question 16

Define heat of combustion?

Answer 16

Energy change of a reaction when a substance is burnt

Question 17

Define Activation energy (Ea)?

Answer 17

The energy needed to initiate a reaction

Question 18

What happens if activation energy is not met?

Answer 18

If the particles collide with less energy than the activation energy then they will not react

Question 19

Is bond breaking an endothermic or exothermic process?

Answer 19

Endothermic

Question 20

Explain why every chemical reaction must have an activation energy, even though for some reactions it might have a low value?

Answer 20

Every chemical reaction needs some amount of activation energy to overcome the forces of repulsion and to begin the reaction.