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WAEC questions for "Chemistry :: Energy and Energy Changes"
Q1

In a chemical reaction, ΔH is positive when

A

H(product)>H(reactant)

B

H(product)(reactant)

C

H(product)=H(reactant)

D

H(product)= Zero

E
Q2

Consider the reaction represented by the following equation: H2(g)+ O2(g)→ H2O(g)ΔH = -285.8Kj mol-1 ΔH represents enthalpy of

A

formation

B

hydration

C

neutralization

D

solution

E
Q3

The collision theory proposes that

A

reactants collide more frequently to bring about reduction in the reaction rate

B

all collisions of reactants are effective

C

reactants must collide with a certain amount minimum amount of energy to form products

D

the fewer the collisions the faster the reaction rate

E
Q4

Which of the following set of equations could be used to represent the standard enthalpy of formation of glucose?

A

6C(s) + 6H2(g) + 3O2(g) → C6H12O6(s)

B

6CO2(g) + 6H2O(l) → C6H12O6(s) + 6O2(g)

C

6C(g) + 6H2(g) + 3O2(g) → C6H12O6(s)

D

6C(g) + 6H2(g) + 3O2(g) → C6H12O6(aq)

E
Q5

Enthalpy change of the reaction is represented by

A

W

B

X

C

Z

D

Y

E
Q6

What type of reaction is represented by the energy diagram?

A

Endothermic

B

Exothermic

C

Redox

D

Neutralization

E
Q7

Consider the reaction represented by the following equation: N2(g) + 3H2(g) ΔH = -92 Kj mol-1 . Finely divided iron is used as catalyst in the reaction in order to

A

lower the value of ΔH

B

increase the time for attainment of equilibrium

C

shorten the time for attainment of equilibrium

D

decrease the yield of ammonia

E
Q8

Consider the reaction represented by H+(aq)+ OH-(aq)→ H2O(l). The energy change taking place in the reaction above is enthalpy of

A

formation

B

hydration

C

neutralization

D

solution

E
Q9

Which of the following processes is an endothermic reaction?

A

Dissolving NH4Cl in water

B

Adding of concentrated H2SO4 in water

C

Dissolving NaOH pellets in water

D

Passing SO3 gas into water

E
Q10

Consider the equation for the equilibrium reaction. 2SO2(g) + O2(g) ↔ 2SO3(g) ΔH = -92Kj mol-1. Which of the following conditions will not increase the yield of sulphur (IV) oxide?

A

Increase in temperature

B

Decrease in temperature

C

Increase in pressure

D

Addition of O2 in the mixture

E
Q11

The activation energy of a reaction can be altered by

A

adding a reducing agent

B

applying high pressure

C

using a catalyst

D

change the temperature

E
Q12

When X is heated with manganese (VI) oxide, oxygen is produced. X is

A

KCl

B

KClO3

C

CaCO3

D

ZnCO3

E
Q13

Which of the following statement is true of an endothermic reaction?

I Heat is absorbed from the surrounding

II The heat content of the products is more than that of the reactants

III The enthalpy change is positive

IV The surrounding is at lower temperature than the system

A

I only

B

I and II only

C

I, II and III only

D

I, II, III and IV

E
Q14

Which of the follwoing are required to in an experiment to determine the enthalpy of solution of anhydrous CuSO4?

I Mass of the anhydrous CuSO4

II Volume of water in which the CuSO4 is dissolved

III Initial temperature of water

IV Final temperature of the solution

A

I and II only

B

III and IV only

C

II, III and IV only

D

I, II, III and IV

E
Q15

Which of the following statements about an exothermic reaction is correct?

A

The products have less heat content than the reactants

B

The system absorbs heat from the surrounding

C

The activation energy is hgh

D

The enthalpy change is positive

E
Q16

What does ΔH mean in the following equation? Cl(g) + e- → Cl-(g) ; ΔH = -363 KJmol-1

A

Ionization energy

B

Electron affinity

C

Dissociation energy

D

Heat of atomization

E
Q17

Consider the following equation. Ag+(aq) + Cl-(aq) → Ag+Cl(s) ; ΔH = -65.7 Kjmol-1. From the equation, it can be deduced that

A

direct combination is involved and the reaction is endothermic

B

a solid is formed and heat is evolved

C

activation energy is high and catalyst is required

D

the reaction is endothermic and occurs at high temperature

E
Q18

A reaction is represented by the equation; A2(g) + B2(g) ↔ 2AB(g) ; ΔH = X KJmol-1. Which of the following statements about the system is correct?

A

The forward reaction is exothermic

B

The reaction goes to completion at equilibrium

C

Pressure has no effect on the reaction mixture

D

At equilibrium, increase in temperature favours the reverse reaction

E
Q19

An exothermic reaction is one which involves

A

attainment of dynamic equilibrium

B

loss of heat to the surrounding

C

evolution of gas as it proceeds

D

positive change in value of enthalpy

E
Q20

Which of the following will decrease in mass when heated in air?

I Magnesium ribbon

II Powdered sulphur

III Calcium trioxocarbon (IV)

IV Magnesium tetraoxosulphate (VI) heptahydrate

A

IV

B

I and II

C

III and IV

D

I, II and III

E

I, II, III and IV

Q21

If the value of ΔH of reaction is negative; it means that the reaction is

A

slow

B

exothermic

C

spontaneous

D

irreversible

E

not feasible

Q22

How much heat will be liberated if 8g of hydrogen burns in excess oxygen according to the following equation? 2H2 + O2 → 2H2O, ΔH = -571.7 kj (H = 1)

A

142.9kj

B

285.9kj

C

571.7kj

D

1143.4kj

E

2286.8kj

Q23

What does X represent in the following equation?

H2(g) + O2(g) → H2O(l) ;ΔH = Xkj

A

Bond energy

B

Activation energy

C

Ionization energy

D

Enthalpy of neutralization

E

Enthalpy of formation

Q24

Which of the following can be deduced from the equation below?

XY(aq) + PQ(aq) → XQ(s) + PY(aq) ΔH = 65,700J

I The heat content of the reactants is higher than that of the products

II. The reaction involves double decmposition

III The reaction is slow

IV A large amount of heat is absorbed

A

IV

B

I and II

C

III and IV

D

I, II and III

E

I, II, III and IV

Q25
If the change in free energy (Dg) of a reaction is negative, it can be deduced that the reaction will I not proceed in the direction indicated II be reversible III not occur at room temperature IV be feasible
A
IV
B
I and II
C
III and IV
D
I, II and III
E
I, II, III and IV
Q26

H3O+(aq) + OH-(aq) → 2H2O(l). The heat change accompanying the reaction represented by the equation is the heat of

A

neutralization

B

formation

C

solution

D

dilution

E

hydration

Q27

A measure of the degree of disorder in a chemical system is known as the

A

enthalpy

B

free energy

C

activation energy

D

entropy

E

equilibrium

Q28

In which of the following changes is ΔS negative?

A

H2O(l) → H2O(s)

B

C(s) + O2(g) → CO(g)

C

PCl5(g) → PCl3(g) + Cl2(g)

D

NaCl(s) → Na+(aq) + Cl-(aq)

E

NH4Cl(s) → NH3(g) + HCl(g)

Q29

If a reaction is said to exothermic, which of the following statement is a correct deduction from the information?

A

The reaction vessels gets hotter as the reaction proceeds

B

ΔH for the reaction is positive

C

The rate of the reaction increases with time

D

The activity energy of the reaction is high

E
Q30

Which of the processes represented by the following equations has the greatest positive entropy change?

A

C6H6(l) + C6H6(g)

B

H2O(s)→ H2O(l)

C

CuO(s) + H2(g) → Cu(s) + H2O(l)

D

Na2CO3(s) + nH2O(l) → Na2CO3 + nH2O(s)

E

S(s) → S(l)

Q31

CH4(g) + 2O2(g) → 2H2O(l) + CO2(g) ΔH = 890KJ Mol -1 ΔH in the reaction represented by the equation is the enthalpy of

A

formation

B

combustion

C

solution

D

activation

E

neutralization

Q32

Consider the reaction represented by the equation below:

H2(g) + I2(g) ↔ 2HI(g) ΔH negative. Which of the following takes place when temperature of the reaction vessel is decreased?

A

The gas condenses

B

The yield of hydrogen increases

C

The concentration of reactants remains constant

D

More of the hydrogen iodide decomposes

E

The yield of hydrogen iodide increases

Q33

The heat accompanying the reaction represented by the equation H2O(l) + H2O(g) is described as the heat of

A

solution

B

neutralization

C

vapourization

D

sublimation

E

activation

Q34

Which of the following correctly explains entropy?

A

The natural tendency for a system to achieve a greater disorder

B

A balance of the driving forces between free energy and enthalpy changes

C

The cause of spontaneity of a reaction

D

A measure of the enthalpy of a reaction

E

A measure of the rate of attainin equilibrium in reversible reaction

Q35

Given that for the reaction KOH(aq) + HCl (aq) → KCl(aq) + H2O(l). H = -54Kjmol-1 What is the quantity of heat evolved in the reaction

2NaOH(aq) + H2SO4(aq) → Na2SO4 + 2H2O(l)?

A

-108kj

B

-54kj

C

-27kj

D

+27kj

E

+54kj

Q36

Given for the reaction, N2(g) + 3H2(g) → 2NH3(g) ΔH = 92kj. What is the enthalpy of the formation of ammonia from its element?

A

- 46 kj mol-1

B

- 184 kj mol-1

C

-92 kj mol-1

D

+ 184 kj mol-1

E

+ 46 kj mol -1

Q37

Which of the following is not decomposed by heat?

A

CaCO3

B

CuCO3

C

ZnCO3

D

NaCO3

E

MgCO3

Q38

The reaction represented by the equation C(S) + H2O(l) → CO(s) + H2(s) was carried out at 270C. If the enthalpy change was +4,500J and the entropy change was +12J. What was the free energy change? (ΔG = ΔH - TΔS)

A

-4176J

B

+4176J

C

-900J

D

+900J

E

+8,100J