Chemistry Chapter on Composition and Reactions

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Questions and Answers

What is the percentage of iron (Fe) in iron(III) oxide (Fe2O3)?

66.67%

72.00%

69.92% (correct)

70.25%

How many moles are present in a 125 g sample of aluminum (Al)?

6.25 moles

5.00 moles

3.41 moles

4.63 moles (correct)

What is the empirical formula of a compound if its molecular formula is C6H12?

C2H4

CH2

C6H12

C3H6 (correct)

How many carbon atoms are in 1.0 carat of diamond, given that 1 carat is 0.2 g?

1.003 x 10^22 Signup and view all the answers

Which of the following statements regarding the mass percentage of a compound is true?

Mass% A = (mass of A / mass of the whole) × 100 is a universal formula. Signup and view all the answers

What is the rate law expression for the reaction of nitric oxide with Br2?

r = K[NO]^2[Br2]^1 Signup and view all the answers

How is the value of x determined from the experimental data?

By comparing rates with the same concentration of Br2 and different concentrations of NO. Signup and view all the answers

If the concentration of Br2 is doubled while keeping the concentration of NO constant, how does the rate of reaction change?

The rate doubles. Signup and view all the answers

What value does y represent in the rate law, based on the provided data?

The order of the reaction with respect to Br2. Signup and view all the answers

In which experimental setup can the value of x be calculated effectively?

From two experiments where only the concentration of NO varies and Br2 is constant. Signup and view all the answers

What does the double arrow in a chemical reaction signify?

The reaction can proceed in both the forward and reverse directions. Signup and view all the answers

At equilibrium, what is true about the rates of the forward and reverse reactions?

The rate of the forward reaction equals the rate of the reverse reaction. Signup and view all the answers

What does a large value of $K_c$ indicate about a chemical reaction?

The forward reaction is fairly complete. Signup and view all the answers

Which of the following factors does NOT affect the numerical value of the equilibrium constant $K$?

Changes in the amounts of substances in equilibrium. Signup and view all the answers

In the reaction $jA (g) + kB (g) \rightleftharpoons mC(g) + nD(g)$, how is the equilibrium constant $K$ defined?

As the ratio of products to reactants at equilibrium. Signup and view all the answers

If the reaction results in a small value of $K_c$, what does it indicate?

The reverse reaction is favored. Signup and view all the answers

In a reaction with steps, which statement is correct regarding determining the equilibrium?

It does not account for intermediate products. Signup and view all the answers

In the law of mass action for a reaction $jA + kB \rightleftharpoons mC + nD$, how can the equilibrium condition be expressed?

At equilibrium, $Kf[A]j[B]k = Kb[C]m[D]n$. Signup and view all the answers

What will happen to the equilibrium position if H2 or I2 is removed from the reaction H2(g) + I2(g) ⇌ 2 HI(g)?

The reaction will shift towards decomposition of HI. Signup and view all the answers

In the reaction SO2(g) + 2 O2(g) ⇌ 2 SO3(g), how does increasing pressure affect the equilibrium position?

It shifts the equilibrium to the right. Signup and view all the answers

For a reaction where the change in the number of moles of gas ( $\Delta n$) is zero, what effect does changing the pressure have?

It has no effect on the equilibrium position. Signup and view all the answers

In an exothermic reaction with a negative $ \Delta H$ value, what is the effect of increasing temperature?

It shifts the equilibrium toward the reactants. Signup and view all the answers

For which of the following reactions would increasing the temperature favor the forward reaction?

CO2 + H2 ⇌ CO + H2O, $ \Delta H = +41.2 KJ$. Signup and view all the answers

What effect does adding a catalyst have on a chemical equilibrium?

It speeds up the rate of reaching equilibrium without changing the position. Signup and view all the answers

What is the effect of adding an inert gas to a system at equilibrium?

It has no effect on the position of the equilibrium. Signup and view all the answers

Which statement is true regarding changes in temperature and their effects on equilibrium?

Increasing the temperature favors endothermic reactions. Signup and view all the answers

What happens to the rate of reaction as the concentration of the reactants increases?

The rate of reaction increases. Signup and view all the answers

Which of the following factors does NOT affect the rate of a chemical reaction?

Volume of the reaction container Signup and view all the answers

In the equation Rate = $-rac{1}{2} rac{ riangle[A]}{ riangle t}$, what does the '2' indicate?

Two moles of A disappear for each mole of B produced. Signup and view all the answers

What effect does a catalyst have on a chemical reaction?

It increases the rate of the chemical reaction. Signup and view all the answers

When considering the reaction 4NH3 + 5O2 -> 4 NO + 6 H2O, if ammonia reacts at a rate of 0.24 mole.L-1.s-1, what is the rate at which O2 reacts?

0.12 mole.L-1.s-1 Signup and view all the answers

Which statement is true regarding the relationship between surface area and reaction rate?

Increased surface area typically increases the reaction rate. Signup and view all the answers

In the context of reaction rates, what is the 'order of the reaction' related to?

It indicates the effect of concentration on rate. Signup and view all the answers

What does the rate constant 'K' depend on in a rate law?

The temperature of the system Signup and view all the answers

Study Notes

Percentage composition of compounds

The mass percentage of a component A can be found by dividing the mass of A by the total mass and multiplying by 100.
For example, in Fe2O3, the percentage of Fe is 69.92%.

Empirical formula and Molecular formula

The simplest formula of a compound is called the empirical formula.
The molecular formula is a multiple of the empirical formula.

Classification of reactions

Reactions can be classified as reversible or irreversible.
In a reversible reaction, reactants react to become products and vice versa.
At equilibrium, the rate of the forward reaction equals the rate of the backward reaction.

Law of mass action

The rate of a reaction is proportional to the product of the concentrations of the reactants raised to their respective stoichiometric coefficients.
The equilibrium constant Kc is the ratio of the rate constants for the forward and reverse reactions.
Kc is influenced by temperature but not by the amounts of substances used or pressure changes.
A large Kc value indicates a reaction that proceeds mostly to completion, while a small Kc indicates a reaction that favors the reverse reaction.
Kc can be affected by temperature changes as well as by removing or adding specific components.

Le Chatelier’s principle

The position of equilibrium in a reversible reaction is affected by changes in temperature, pressure, or concentration.
Increasing the pressure (or decreasing the volume) shifts the equilibrium towards the side with fewer moles of gas.
Increasing the temperature favors the endothermic reaction, while decreasing the temperature favors the exothermic reaction.
The addition of a catalyst increases the speed at which equilibrium is reached but does not affect the equilibrium position.
Adding an inert gas has no effect on the equilibrium position.

Reaction rates & their measurements

The rate of a reaction is expressed as the change in concentration of a reactant or product over time.
The stoichiometry of the reaction must be considered when calculating reaction rates.

Factors affecting the rate of chemical reaction

Nature of the reactants: Some reactants react faster than others.
Surface area: Increasing the surface area of reactants increases the rate of the reaction.
Temperature: The rate of a reaction generally increases with temperature.
Catalyst: Catalysts speed up reactions but do not affect the equilibrium position.
Concentration: Increasing the concentration of reactants generally increases the rate of the reaction.

Rate laws

The rate of a reaction is often proportional to the product of the concentrations of the reactants raised to some power.
This relationship is known as the rate law.
The rate constant K is a constant that is affected by temperature.

Determining the rate law

By analyzing experimental data on reaction rates at different reactant concentrations, the rate law can be determined.
To find the order of the reaction with respect to a particular reactant, compare the rates of experiments where the concentration of that reactant changes while other concentrations are kept constant.
The order of the reaction is the value that makes the rates consistent.

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Test your knowledge on the percentage composition of compounds, empirical and molecular formulas, and the classification of chemical reactions. Understand key concepts such as the law of mass action and equilibrium constants. Perfect for students looking to deepen their chemistry understanding.