Edexcel IGCSE Chemistry: Chemical Equations
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Questions and Answers

What fundamental principle of chemical reactions is highlighted regarding atoms?

  • Atoms are destroyed during product formation.
  • The total number of atoms changes during a reaction.
  • Atoms can be created during a reaction.
  • Atoms are only rearranged in chemical reactions. (correct)

In a chemical equation, if a substance is present in the reactants, where must it be found?

  • In both reactants and products. (correct)
  • In a solid state in the products.
  • In the gaseous state in the products.
  • In the products only if it is transformed.

What does it mean when it is stated that atoms cannot be created or destroyed?

  • Chemical reactions do not involve any form of atomic conversion.
  • Atoms remain unchanged throughout a reaction.
  • Atoms can be lost if they escape into the environment.
  • Atoms from reactants are accounted for in products through rearrangement. (correct)

Why is it essential to account for all atoms in chemical reactions?

<p>To fulfill the requirements of chemical stoichiometry. (C)</p> Signup and view all the answers

What happens to the total mass of reactants and products in a closed system during a chemical reaction?

<p>The total mass remains unchanged. (D)</p> Signup and view all the answers

What is the relative formula mass of sodium chloride (NaCl)?

<p>58.5 (C)</p> Signup and view all the answers

Which of the following represents the correct calculation for the relative formula mass of magnesium nitrate (Mg(NO3)2)?

<p>24 + (14 x 1 x 2) + (16 x 3 x 2) (B)</p> Signup and view all the answers

What unit is used to measure chemical amounts in the context of moles?

<p>moles (A)</p> Signup and view all the answers

What is the significance of the Avogadro constant in chemistry?

<p>It represents the number of molecules in a mole of a substance. (D)</p> Signup and view all the answers

Which statement is true regarding the relative atomic mass listed on the Periodic Table?

<p>It represents the average mass of an element's isotopes. (D)</p> Signup and view all the answers

What is the correct unit for expressing concentration when using moles of solute?

<p>mol/dm3 (D)</p> Signup and view all the answers

If a solution has a higher concentration, what does it imply about the amount of solute?

<p>There is more solute in a given volume. (A)</p> Signup and view all the answers

Which part of a solution is generally referred to as the solute?

<p>A solid substance that dissolves in a liquid. (C)</p> Signup and view all the answers

How is the concentration of a solution calculated in moles per dm3?

<p>Number of moles of solute divided by volume of solution. (A)</p> Signup and view all the answers

In the context of solutions, which statement describes a solvent?

<p>The liquid in which the solute dissolves. (A)</p> Signup and view all the answers

What is the molar mass of nitrogen gas (N2)?

<p>28 g/mol (A)</p> Signup and view all the answers

How many moles of nitrogen are present in 154 g of nitrogen gas?

<p>5.5 mol (C)</p> Signup and view all the answers

According to the balanced equation for the combustion of propane, how much oxygen is needed to react with 150 cm³ of propane?

<p>750 cm³ (B)</p> Signup and view all the answers

What is the total volume of gaseous products produced from the complete combustion of 150 cm³ of propane?

<p>1050 cm³ (A)</p> Signup and view all the answers

What is important to remember when calculating reacting gas volume questions?

<p>Use the correct units as asked by the question (B)</p> Signup and view all the answers

What is the term used to describe the amount of product obtained from a reaction?

<p>Reaction yield (D)</p> Signup and view all the answers

Which of the following is NOT a reason for not achieving 100% yield in a chemical reaction?

<p>Accurate measurements (C)</p> Signup and view all the answers

How is percentage yield calculated?

<p>Actual yield divided by theoretical yield times 100 (B)</p> Signup and view all the answers

What is the actual yield?

<p>The yield recorded from the reaction (C)</p> Signup and view all the answers

For chemical companies, having a high percentage yield is important primarily for which reason?

<p>To increase profits and reduce costs (A)</p> Signup and view all the answers

In cases of reversible reactions, what impact does it have on yield?

<p>It prevents achieving a high yield (A)</p> Signup and view all the answers

During which stage might product loss occur due to physical handling?

<p>During transfer between containers (A)</p> Signup and view all the answers

What is the primary purpose of measuring percentage yield in chemical processes?

<p>To determine the efficiency of the reaction pathway (C)</p> Signup and view all the answers

How many moles of HCl are required to react with 0.00125 moles of Na2CO3?

<p>0.00250 moles (B)</p> Signup and view all the answers

What is the concentration of HCl in mol/dm3 if 0.00250 moles are present in 20 cm3?

<p>0.125 mol / dm3 (B)</p> Signup and view all the answers

What volume does one mole of gas occupy at room temperature and pressure?

<p>24.0 dm3 (D)</p> Signup and view all the answers

What is the correct way to convert 20 cm3 to dm3?

<p>Divide by 1000 (B)</p> Signup and view all the answers

Which of the following statements correctly describes Avogadro's Law?

<p>Equal volumes of gases contain equal numbers of particles at the same temperature. (A)</p> Signup and view all the answers

How many moles of Na2CO3 would be needed to completely react with 0.00500 moles of HCl?

<p>0.00250 moles (A)</p> Signup and view all the answers

What is the result of 25.0 cm3 when converted to dm3?

<p>0.025 dm3 (B)</p> Signup and view all the answers

What determines the volume at which gases occupy at the same conditions, according to Avogadro's Law?

<p>Temperature and pressure (B)</p> Signup and view all the answers

Flashcards

Law of Conservation of Mass

Chemical reactions always involve the rearrangement of existing atoms into new substances. No new atoms are created, and none are destroyed.

Chemical Equation

A symbolic representation of a chemical reaction using chemical formulas and symbols.

Reactants and Products in a Chemical Equation

The chemical formulas of the reactants are written on the left side of the arrow, and the formulas of the products are written on the right side.

Balancing Coefficients

The numbers in front of each chemical formula in a balanced equation represent the number of moles of each reactant and product involved in the reaction.

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Balancing Chemical Equations

Adjusting the coefficients in a chemical equation to ensure that the number of atoms of each element on the reactant side equals the number of atoms of that element on the product side.

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What is Relative Formula Mass?

The relative formula mass (RFM) is the sum of the relative atomic masses (RAM) of all the atoms in a chemical formula. Use the periodic table to find the RAM of each element.

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What is a mole?

A mole is a unit of measurement that represents a specific number of particles. One mole contains 6.022 x 10^23 particles (atoms, ions, molecules). This number is known as Avogadro's constant.

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What is Avogadro's Constant?

The Avogadro constant represents the number of particles (atoms, molecules, or ions) in one mole of a substance. It is approximately 6.022 x 10^23 particles per mole.

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What is Relative Atomic Mass (RAM)?

The relative atomic mass (RAM) of an element is the average mass of an atom of that element compared to the mass of a carbon-12 atom. The RAM is found on the periodic table.

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How is a mole used to express the amount of substance?

The mole is used to express the amount of substance. One mole of any substance contains the same number of particles as one mole of any other substance.

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Actual Yield

The amount of product you actually obtain from a reaction in an experiment.

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Theoretical Yield

The maximum amount of product that could be formed from a given amount of reactants, assuming ideal conditions.

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Percentage Yield

The percentage of the theoretical yield that is actually obtained in a reaction.

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Reaction Pathway

A series of chemical reactions designed to produce a desired product.

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Equilibrium

A reversible reaction reaches a point where the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in concentration of reactants or products.

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Reversible Reaction

A reaction that can proceed in both directions, meaning the products can react to form reactants and vice versa.

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Loss of Product

Loss of product during separation and purification stages, such as filtration or distillation.

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Side Reactions

Reactions that occur alongside the main reaction, often forming undesirable byproducts, and decrease the overall yield of the desired product.

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Concentration of a Solution

The amount of solute dissolved in a specific volume of solvent. It indicates the solute's concentration.

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What is a solute?

The solid substance that dissolves in a liquid to form a solution.

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What is a solvent?

The liquid in which a solute dissolves to form a solution.

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What is a solution?

The mixture formed when a solute dissolves completely in a solvent.

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How is concentration calculated?

The amount of substance per unit volume, typically expressed in moles per cubic decimeter (mol/dm3).

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Molar Volume

The volume occupied by one mole of any gas at standard temperature and pressure (STP).

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What is the molar gas volume at RTP?

The amount of gas that one mole of any gas occupies at room temperature and pressure (RTP). It is usually given as 24 dm3 or 24,000 cm3.

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What is Avogadro's Law?

A law stating that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules.

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What is a reversible reaction?

A reaction that can proceed in both directions. The products can react to form reactants, and vice versa. The rate of the forward reaction equals the rate of the reverse reaction.

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What is the theoretical yield?

The maximum amount of product that could be formed from a given amount of reactants, assuming ideal conditions.

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What is the actual yield?

The amount of product you actually obtain from a reaction in an experiment.

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What is percentage yield?

The percentage of the theoretical yield that is actually obtained in a reaction.

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How to calculate the volume of a Gas?

A method for calculating the volume of a gas when given the number of moles and vice versa.

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What are RTP conditions?

A set of conditions used in gas calculations, typically 20 °C and 1 atmosphere (atm).

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Study Notes

Edexcel IGCSE Chemistry: Chemical Formulae, Equations, Calculations

  • This document covers word equations, chemical equations, relative mass calculations, moles, reacting masses, percentage yield, compound formulae determination, empirical and molecular formulae, solution concentrations, and gas volumes.

  • Chemical reactions involve the rearrangement of atoms.

  • Atoms cannot be created or destroyed during a chemical reaction. The mass of the reactants equals the mass of the products.

  • Word equations use names of substances, while symbol equations use their chemical formulae.

  • Reactants are on the left, products on the right, with an arrow separating them.

  • State symbols (s, l, g, aq) indicate the physical state (solid, liquid, gas, aqueous solution.)

  • Balancing equations ensures equal numbers of each atom type on both sides of the arrow, following the Law of Conservation of Mass.

  • Relative formula mass (Mr) reflects the sum of the relative atomic masses (Ar) of all atoms in a molecule or formula unit of a substance

  • Moles, mass, and molar mass are interconnected through the formula triangle: (mass = moles x molar mass; moles=mass / molar mass; molar mass = mass/moles)

  • Molar mass is the mass of one mole of a substance in grams.

  • The Avogadro constant (6.02 x 1023 mol-1) represents the number of atoms, molecules, or ions in one mole of a substance.

  • Percentage yield = (actual yield/theoretical yield) x 100%

  • Calculating percentage yield accounts for practical limitations in chemical reactions (e.g., incomplete reactions, side reactions, losses in handling).

  • Empirical formulas provide the simplest whole number ratio of elements in a compound, while molecular formulas show the actual number of each element.

  • Calculating empirical formulas involves determining the ratios of elements in a compound from experimental data (e.g., mass measurements).

  • Calculating molecular formulas requires determining the empirical formula and the compound's molar mass.

  • Determining the formula of a hydrated salt often needs heating to remove water.

  • Calculating the formula of a metal oxide using combustion involves measuring masses before and after a reaction to find ingredient ratios.

  • Calculating the formula of copper(II) oxide often involves reduction with methane.

  • Concentration (or strength) of a solution is expressed as the amount of solute (in grams or moles) dissolved in a specific volume (cm³ or dm³) of the solvent.

  • The concentration unit of mol/dm³ provides a convenient way of calculating the number of moles from a solution's volume and concentration.

  • The molar volume of a gas at room temperature and pressure (RTP) is 24 dm3 mol-1

  • The gas volume can be calculated using the formula: (volume = moles x molar volume).

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Description

This quiz covers the essentials of chemical formulae, equations, and calculations relevant to the Edexcel IGCSE Chemistry syllabus. You'll explore topics such as balancing equations, relative mass, moles, and the Law of Conservation of Mass. Prepare to test your knowledge of both word and symbol equations as well as practical calculations involving chemical substances.

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