Equilibrium and Chemical Energy

Question 1

when does a reaction reach an equilibrium

Answer 1

when the rate of the forward reaction equals the rate of the reverse reaction

Question 2

what are the concentrations of reactants and products when at equilibrium

Answer 2

they’re constant

Question 3

what do catalysts do to an equilibrium

Answer 3

catalysts increase the rate at which an equilibrium is formed but do not effect the position of the equilibrium

Question 4

what is Le Chatelier’s Principle

Answer 4

an equilibrium or move to undo any change imposed upon it by temporarily favouring, either the forward or backward reaction until the new equilibrium position is reached

Question 5

what do you say when the forward reaction is favoured

Answer 5

the equilibrium has moved to the right

Question 6

what do you say when the backward reaction is favoured

Answer 6

the equilibrium has moved to the left

Question 7

what does increasing temperature do to the equilibrium

Answer 7

increase in the temperature will cost equilibrium to move to decrease the temperature

Question 8

what do High temperatures favour

Answer 8

endothermic reactions

Question 9

what do low temperatures favour

Answer 9

exothermic reactions

Question 10

what factors affect equilibrium

Answer 10

• concentration
• temperature
• pressure
• catalyst

Question 11

what does increasing pressure do to the equilibrium

Answer 11

increasing the pressure, because the equilibrium to move to decrease the pressure. The equilibrium will move to reduce the number of gas particles.

Question 12

what does decrease in the pressure do to the equilibrium

Answer 12

Decreasing the pressure will cause the equilibrium to move to increase the pressure. The equilibrium will move to increase the number of gas particles

Question 13

what does high pressure favour

Answer 13

the side with less gaseous moles

Question 14

what does low pressure favour

Answer 14

more gaseous moles

Question 15

what does increasing the concentration of a chemical do to the equilibrium

Answer 15

increase in the concentration of a chemical will cause the equilibrium to move to use up the chemical. This shifts, the equilibrium to the opposite side.

Question 16

what does decreasing the concentration do to the equilibrium

Answer 16

A decrease in the concentration of the chemical will cause the equilibrium to move to form the chemical. This shifts the equilibrium to the reaction that makes the chemical.

Question 17

what is enthalpy

Answer 17

a measure of the energy stored in a chemical

Question 18

chemistry energy formula

Answer 18

Eh=cm/\T

c=4.18
m=mass of water(KG)
/\T=change in temperature

Question 19

what does Hess’s law state

Answer 19

the overall enthalpy charge for a reaction is the same regardless of the route taken

Question 20

what is the enthalpy of formation

Answer 20

the energy needed to make one mole of a compound from its elements in their standard form

Question 21

what is bond enthalpy for diatomic molecules

Answer 21

for a diatomic molecule, XY, the molar bond enthalpy is the energy required to break one mole of bones

Question 22

what kind of reaction is bond breaking

Answer 22

endothermic (XY——>X+Y)

Question 23

what kind of reaction is bond making

Answer 23

exothermic (X+Y——>XY)

Question 24

what can the bond enthalpy be affected by

Answer 24

The bonding to be will be affected by the environment the bond is in, so a C-H bond in methane may have a slightly different bond enthalpy from one of propene

Question 25

steps for calculating bond enthalpy

Answer 25

1. draw the full structural formula of all molecules in the equation
2. make a list of all the bonds being broken in the reactants
3. fill in the bond enthalpies
4. repeat steps 2&3 for the bonds made in products
5. add up the total enthalpies for bond breaking and making (bond making is always negative due to it being exothermic)
6. calculate the overall enthalpy change