enthalpy

Question 1

What are chemical bonds?

Answer 1

They are the forces of attraction that bind atoms together

And chemical energy lies within these bonds, this is a form of potential energy

Question 2

what is the conservation of energy?

Answer 2

In chemical reactions, energy is changed from one form to another :
Chemical energy-> thermal energy

No energy is lost as it is converted from one form to another

Question 3

What are some factoids enthalpy?

Answer 3

Enthalpy (H) is the thermal energy that is stored in a system

Fun Fact: we can’t measure the direct enthalpy of profits and reactants so instead we can measure the amount of energy that is absorbed or released to the surroundings (e.g. water in the eq, Q=mc(delta)T)
This can be done by looking at the change in thermal energy.

Question 4

In calorimetry what does heat gain to the surroundings mean?

Answer 4

Exothermic, there is heat loss in a chemical system

Question 5

In calorimetry what does heat loss to the surroundings mean?

Answer 5

Endothermic, heat gain in the chemical system

Question 6

What is enthalpy change?

Answer 6

Enthalpy change is the heat energy change at a constant pressure

Question 7

In delta H power theta, what does theta indicate?(pimsole sign)

Answer 7

Standard conditions I’m either pressure (100KPa) or temperature (298K)

Question 8

what are standard states?

Answer 8

They are the states which substances are under in standard conditions
E.g. the standard state of water is liquid and the standard state of magnesium is solid

Question 9

What is a system?

[these are part of the terminology used to discuss components of chemical reactions]

Answer 9

A system is the atoms and bonds involved in a chemical reaction (like in the le chat principle from equilibrium)

Question 10

What is the surroundings?

Answer 10

Everything else besides the system

Question 11

what does exothermic mean?

Answer 11

A reaction which releases thermal energy to the surroundings as the products have less energy than the reactants.

(Nether world)

Question 12

What does endothermic mean?

Answer 12

When thermal energy is absorbed from the surroundings into the reaction as the products have more energy than the reactants.
( Endermen)

Question 13

what is the exothermic reaction profile?

Answer 13

• the enthalpy of the products

Question 14

What is the reaction profile of endothermic reactions?

Answer 14

• the chemical reaction absorbs heat
• there is a heat gain from the surroundings
• the enthalpy of the products > reactants
• enthalpy change is positive

Question 15

What is activation energy?

Answer 15

The minimum energy required to start a reaction

Question 16

Why does there have to be an input of energy in exothermic reactions?

Answer 16

Although the products have a lower energy than the reactants, the input of energy is required to break the initial bonds to start the reaction. Once the activation energy has been overcome the energy output of the reaction provides enough energy to sustain the reaction
As a result the reaction becomes self sustaining

Question 17

why does there have to be an input of energy in endothermic reactions?

Answer 17

The products have a higher energy than the reactants so nothing happens unless heat is added to the reaction

Question 18

What is the enthalpy change of formation?

Answer 18

The energy change that takes the place when one mole of a compound is formed from it’s constituent elements in their standard state under standard conditions
E.g. Li(s)+1/2 F2(g)-> LiF(s)

Question 19

What is the enthalpy change of combustion?

Answer 19

The energy change that takes place when one mole of a substance is completely combusted.
E.g. H2(g) +1/2 O2 (g) ->H2O(l)

Question 20

What is the enthalpy change of neutralisation?

Answer 20

The energy change associated with the formation of one mole of water from a neutralisation reaction under standard conditions
E.g. HCl(aq) + NaOH (aq) -> NaCl(aq) +H2O(l)

Question 21

To sum up just rebook at the chapter about reversible reactions and equilibrium

Answer 21

Xoxo