Energy Transfer

Question 1

what is an exothermic reaction

Answer 1

a reaction which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise of temperature of the surroundings

Question 2

what is an endothermic reaction

Answer 2

a reaction which takes in energy from the surroundings usually in the form of heat, usually in the form of heat and usually shown by a fall in temperature of the surroundings

Question 3

what is enthalpy change

Answer 3

the overall change in energy in a reaction

Question 4

what does a negative enthalpy change mean

Answer 4

the reaction is exothermic

Question 5

what does a positive enthalpy change mean

Answer 5

the reaction is endothermic

Question 6

formula for heat energy transferred

Answer 6

Q = m x c x change in temp (C)
Q = heat energy transferred (J)
m = mass of liquid being heated (g)
c = specific heat capacity(J/g/degrees C)

Question 7

formula for enthalpy change

Answer 7

total energy absorbed to break bonds - total energy released in making bonds

Question 8

what happens in an endothermic reaction in terms of energy used to break bonds and energy released from forming them

Answer 8

-energy used to break bonds is greater than the energy released by forming them

Question 9

what happens in an exothermic reaction in terms of energy used to break bonds and energy released from forming them

Answer 9

-energy released by forming bonds is greater than the energy used to break them

Question 10

what is a reversible reaction

Answer 10

a reaction where the products of the reaction can react with each other and convert back to the original reactants

Question 11

what is dynamic equilibrium

Answer 11

rate of forward reaction is the same as the rate of backwards reaction

Question 12

conditions for dynamic equilibrium

Answer 12

-closed system(none of the reactants or products can escape)
-constant concentrations of both reactants and products

Question 13

effects of raising the temperature in a reversible reaction

Answer 13

raising the temperature causes the endothermic reaction will increase to use up the extra heat

Question 14

effects of raising the pressure in a reversible reaction

Answer 14

an increase in pressure results in the position of equilibrium shifting in the direction which gives a decrease in the number of gas molecules

Question 15

effect of adding a catalyst on the position of equilibrium

Answer 15

no effect, speeds up the forward and backward reaction by the same amount

Question 16

Find the amount of energy produced per gram of ethanol burnt in a combustion reaction

Answer 16

1. The initial mass of the ethanol and spirit burner is measured and recorded.
2. 100cm3 of water is transferred into a copper container and the initial temperature is measured and recorded.
3. The burner is placed under of copper container and then lit.
4. The water is stirred constantly with the thermometer until the temperature rises by, say, 30 oC
5. The flame is extinguished and the maximum temperature of the water is measured and recorded.
6. The burner and the remaining ethanol is reweighed.

Question 17

describe what happens in the thermal decomposition of ammonium chloride

Answer 17

1. ammonium chloride is heated and breaks down into the gases ammonia and hydrogen chloride
2. let the ammonia and hydrogen chloride(both mix to form white smoke) cool to reform ammonium chloride(white solid)

Question 18

describe what happens in the dehydration of hydrated copper (II) sulphate

Answer 18

1. hydrated copper sulphate(blue) is heated, forming anhydrous copper sulphate(white) and water vapour
2. for the backward reaction add water to the anhydrous copper sulphate