Chemical Reactions and Equations

Comprehensive practice flashcards covering chemical equations, reaction types (combination, decomposition, displacement, redox), and chemical effects like corrosion and rancidity.

What four observations typically indicate that a chemical reaction has taken place?

Change in state, change in colour, evolution of a gas, and change in temperature.

Why is a magnesium ribbon cleaned with sandpaper before burning?

To clean the magnesium ribbon (about $3-4\,cm$ long) of impurities so it can react properly with oxygen.

What is the product of burning magnesium in air, and what is its appearance?

The product is magnesium oxide ($MgO$), which is a white powder formed by the reaction between magnesium and oxygen.

What is the simplest way to describe a chemical reaction in writing?

In the form of a word-equation, such as: Magnesium + Oxygen $\rightarrow$ Magnesium oxide.

Define reactants and products in a chemical reaction.

Reactants are the substances that undergo chemical change (written on the Left-Hand Side), and products are the new substances formed (written on the Right-Hand Side).

What is a skeletal chemical equation?

A chemical equation that is unbalanced because the mass is not the same on both sides, meaning the number of atoms of each element is not equal in the reactants and products.

According to the Law of Conservation of Mass, why must chemical equations be balanced?

Because mass can neither be created nor destroyed in a chemical reaction; therefore, the total mass and the number of atoms of each element must be equal on both sides.

What is the 'hit-and-trial' method of balancing chemical equations?

A method where trials are made to balance an equation using the smallest whole number coefficients.

What do the physical state symbols $(g)$, $(l)$, $(aq)$, and $(s)$ represent?

$(g)$ for gaseous, $(l)$ for liquid, $(aq)$ for aqueous (a solution in water), and $(s)$ for solid.

What is a combination reaction?

A reaction in which a single product is formed from two or more reactants.

Write the chemical equation for the formation of slaked lime from quick lime.

$$CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}$$

What is an exothermic chemical reaction?

A reaction in which heat is released along with the formation of products.

Write the balanced chemical equation for respiration.

$$C_6H_{12}O_6(aq) + 6O_2(aq) \rightarrow 6CO_2(aq) + 6H_2O(l) + \text{energy}$$

How is calcium carbonate ($CaCO_3$) formed on walls after whitewashing?

Calcium hydroxide ($Ca(OH)_2$) reacts slowly with carbon dioxide ($CO_2$) in the air to form a thin layer of calcium carbonate.

What is a decomposition reaction?

A reaction where a single reactant breaks down to give simpler products.

What is thermal decomposition?

A decomposition reaction that is carried out by heating. An example is the decomposition of limestone ($CaCO_3$) into quick lime ($CaO$) and carbon dioxide ($CO_2$).

What happens when lead nitrate is heated as seen in Activity 1.6?

It decomposes to produce lead oxide ($PbO$), oxygen, and brown fumes of nitrogen dioxide ($NO_2$).

What are the two gases produced during the electrolysis of water?

Hydrogen and oxygen; the volume of hydrogen collected is double the volume of oxygen.

What happens to silver chloride when it is placed in sunlight?

It decomposes into silver and chlorine, and its white colour turns grey ($2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$).

Define an endothermic reaction.

A reaction in which energy (in the form of heat, light, or electricity) is absorbed.

What is a displacement reaction?

A reaction where a more reactive element displaces or removes a less reactive element from its compound, such as iron displacing copper from copper sulphate.

Explain double displacement reactions.

Reactions in which there is an exchange of ions between the reactants to form new compounds.

What is a precipitate?

An insoluble substance formed during a chemical reaction, such as the white barium sulphate ($BaSO_4$) formed from sodium sulphate and barium chloride.

Define oxidation and reduction.

Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.

What is a redox (oxidation-reduction) reaction?

A reaction where one reactant gets oxidised while the other gets reduced simultaneously.

Define corrosion and provide an example.

Corrosion is the process where a metal is attacked by substances like moisture or acids. Examples include the rusting of iron, the black coating on silver, and the green coating on copper.

What is rancidity and how can it be prevented?

Rancidity is the oxidation of fats and oils in food, changing their smell and taste. It can be prevented by adding antioxidants, using airtight containers, or flushing food packaging with nitrogen gas.