Ch5: Language of chemistry

 Q4. Define the following terms.

a) Element -  An element is a pure substance that cannot be broken down by any physical or chemical means into simpler substances.

b) Compound - A compound is a substance formed when two or more chemical elements are chemically bonded together. In mixtures, the substances present are not chemically bonded together.

c) Chemical symbols - A chemical symbol is a notation of one or two letters representing a chemical element.  A chemical symbol is a shorthand method of representing an element. Instead of writing out the name of an element, we represent an element name with one or two letters.

d) Chemical formula - A compound is a substance made up of a definite proportion of two or more elements. A chemical formula tells us the number of atoms of each element in a compound. It contains the symbols of the atoms of the elements present in the compound as well as how many there are for each element in the form of subscripts.

e) Molecular Mass -the mass of a molecule that is equal to the sum of the masses of all the atoms contained in the molecule

5. Differentiate between the following

a) Element and compound -

Sl. No.	Differentiating Property	Element	Compound
1	Definition	Elements are pure substances that are composed of only one type of atom.	Compounds are substances that are formed by two or more different types of elements that are united chemically in fixed proportions.
2	Total Numbers	There are nearly 118 elements (at present) of which nearly 94 occur naturally on Earth.	Compounds are almost endless.
3	Types	Elements are classified as either metals, nonmetals, or metalloids.	Compounds are classified according to their bonds which can be ionic, molecular, or metallic.
4	Examples	Some of the examples of elements are Iron, Copper, Gold, etc.	A few examples of compounds are NaOH, NaCl, etc.

b) Chemical reaction and chemical equation

Ans: A chemical reaction is all about chemical change. The ripening of fruits, photosynthesis, tarnishing of iron, burning of woods, digestion of foods, and even cooking foods are few examples of chemical changes and chemical reactions happening around us and even inside our bodies. A chemical reaction involves the transformation of one or more substances into another substance or substances. it involves a change in composition and is represented by a chemical equation.

A chemical equation provides a concise picture of a chemical change. It is used to convey pertinent information about the chemical reaction which includes the substances involved and their quantitative ratio.

Chemical equations are representations of chemical reactions in terms of symbols of elements and formulas of compounds involved in the reactions. The substances that enter into a chemical reaction are called reactants and the substances formed are the products.

c) Reactants and products - In a chemical reaction, substances (elements and/or compounds) called reactants are changed into other substances (compounds and/or elements) called products. You can’t change one element into another in a chemical reaction — that happens in nuclear reactions. Instead, you create a new substance with chemical reactions.

Chemical equations show the reactants and products, as well as other factors such as energy changes, catalysts, and so on. With these equations, an arrow is used to indicate that a chemical reaction has taken place. In general terms, a chemical reaction follows this format:

Reactants→Products

Q7.Answer in brief.

a) What is an element? Give any two characteristics?

Ans:  Any substance that contains only one kind of atom is known as an element. The main characteristics of the elements are as follows:-

1. Atoms cannot be created or destroyed in a chemical reaction, thus elements such as phosphorus (P4) or sulfur (S8) cannot be broken down into simpler substances by the chemical reactions.

Example: Water decomposes into a mixture of hydrogen and oxygen when an electric current is passed through the liquid. Hydrogen and oxygen, on the other hand, cannot be decomposed into simpler substances. They are therefore the elementary, or simplest, chemical substances - elements.

2. Each element is represented by a unique symbol. The notation for each element can be found on the periodic table of elements.

3. The elements can be divided into three categories that have characteristic properties: metals, nonmetals, and semimetals.

b) Write the characteristics of chemical changes?

Ans:  A chemical change produces a new substance. The changes are permanent and mostly irreversible. Also, it involves the absorption or release of energy in the form of heat or light.

c) Calculate the molar mass of MgCo3.

Ans: 24.03 +12.01+(16.00*3) =84.31 grams/mole

d) What is the law of conservation of mass?

Ans: 

• The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations.
• According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.
• The law of conservation of mass is useful for a number of calculations and can be used to solve for unknown masses, such as the amount of gas consumed or produced during a reaction.

e) What is the difference between an element and a compound?

Ans: Given above. 

Q8. 

a) What are the steps involved in balancing a chemical equation?

Ans: 

Step 1: The Unbalanced Chemical Equation

Step 2: Make a List

Step 3: Identifying the Atoms in Each Element

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• Step 4: Multiplying the Number of Atoms

  

• Step 5: Placing Coefficients in Front of Molecules

  

  
  

• Step 6: Check Equation

  

  
  

• Step 7: Balanced Chemical Equation