
i.All decomposition reactions are endothermic. Why?
ii. Why do silver articles become black after sometime when they are exposed to air?
Answer
480k+ views
Hint: When bonds break in a compound, energy is required, whereas, when new bonds are formed, then energy gets released in the form of heat. Silver reacts with a hydrogen compound present in air to form a precipitate.
Complete step by step answer: In order to answer the question, we need to understand the thermodynamics of reaction. When a balanced chemical equation not only indicates the quantities of different reactants and products but also indicates the amount of heat evolved or absorbed ( ) in the reaction is known as the thermochemical equation. The physical state (along with allotropic states) of the substance in an equation is also specified. For example:
The equation represents an exothermic reaction shown by the negative sign of enthalpy change. It describes the combustion of liquid ethanol at constant pressure and temperature. Some important properties of the thermochemical equations are:
i. For exothermic reactions, is negative whereas for endothermic reactions, is positive.
ii. Unless otherwise mentioned, AH values are for the standard state of the substance (i.e. 298 K and 1 bar pressure)
iii. The coefficients of different substances represent the number of moles reacted and formed for the heat change represented in the equation.
iv. The numerical value of refers to the number of moles of substance specified by an equation. standard enthalpy change will have units as
v. The physical state of different substances must be mentioned as the heat evolved or absorbed depends upon the physical state.
vi. If the reaction is reversed, the sign of changes but the magnitude remains the same.
In a decomposition reaction, bonds of a large molecule break to form a small molecule and for this, energy is needed, which makes it endothermic.
ii.) The reactions involving exposure of silver in air are:
This formation is the reason for black layer.
Note: It is to be noted that when a thermochemical equation is multiplied or divided by a constant term, then the enthalpy of the reaction also gets multiplied or divided accordingly.
Complete step by step answer: In order to answer the question, we need to understand the thermodynamics of reaction. When a balanced chemical equation not only indicates the quantities of different reactants and products but also indicates the amount of heat evolved or absorbed (
The equation represents an exothermic reaction shown by the negative sign of enthalpy change. It describes the combustion of liquid ethanol at constant pressure and temperature. Some important properties of the thermochemical equations are:
i. For exothermic reactions,
ii. Unless otherwise mentioned, AH values are for the standard state of the substance (i.e. 298 K and 1 bar pressure)
iii. The coefficients of different substances represent the number of moles reacted and formed for the heat change represented in the equation.
iv. The numerical value of
v. The physical state of different substances must be mentioned as the heat evolved or absorbed depends upon the physical state.
vi. If the reaction is reversed, the sign of
In a decomposition reaction, bonds of a large molecule break to form a small molecule and for this, energy is needed, which makes it endothermic.
ii.) The reactions involving exposure of silver in air are:
This
Note: It is to be noted that when a thermochemical equation is multiplied or divided by a constant term, then the enthalpy of the reaction also gets multiplied or divided accordingly.
Recently Updated Pages
Master Class 11 Business Studies: Engaging Questions & Answers for Success

Master Class 11 Accountancy: Engaging Questions & Answers for Success

Master Class 11 Computer Science: Engaging Questions & Answers for Success

Master Class 11 English: Engaging Questions & Answers for Success

Master Class 11 Social Science: Engaging Questions & Answers for Success

Master Class 11 Economics: Engaging Questions & Answers for Success

Trending doubts
Which one is a true fish A Jellyfish B Starfish C Dogfish class 11 biology CBSE

State and prove Bernoullis theorem class 11 physics CBSE

1 ton equals to A 100 kg B 1000 kg C 10 kg D 10000 class 11 physics CBSE

In which part of the body the blood is purified oxygenation class 11 biology CBSE

One Metric ton is equal to kg A 10000 B 1000 C 100 class 11 physics CBSE

Difference Between Prokaryotic Cells and Eukaryotic Cells
