Chemistry M.C.Q (1 Marks)

When beaten by a hammer the material heats up due to the impact.
As the work done by this heat is zero there is a net increase in internal energy.

The vapor pressure at which a liquid boils is equal to the atmospheric pressure.

In case of saturated vapors, when a certain quantity of heat is removed, the temperature increases.
Hence, the specific heat is negative for saturated vapors.

Internal energy is associated with the atoms or molecules of the gas.
In an ideal gas the energy is in the form of Kinetic energy only.

The reaction of baking soda with other acids, like hydrochloric acid, is also endothermic.
Melting of ice and Evaporation of water is show endothermic process.

The internal energy wil be less due to the short range repulsive forces present between the molecules of the real gas.

In a perfect gas or an ideal gas, the atoms of molecules collide in a perfectly elastic manner. That is the intermolecular attractive forces are absent and thus the internal energy is completely kinetic.

Spontaneous processes are irreversible because they can be reversed only by taking a different path to get back to their original state. A reversible process can take the same path to return to its original state. An irreversible process must take a different path to get back to its original state.

Energy arising by gravitational pull is not included in internal energy. Its external energy.

Thermodynamics is the branch of physics concerned with heat and temperature and their relation to energy and work.
In thermodynamics, we study about the concepts of heat, temperature and relation between heat energy and mechanical energy.

pontaneous combustion is a byproduct of spontaneous heating, which occurs when a material increases in temperature without drawing heat from its surroundings. Such materials have a low ignition temperature. If the material reaches its ignition temperature, spontaneous ignition or combustion occurs.
Examples of materials that are prone to spontaneous combustion include oily rags, hay, and other agricultural products.

Explanation: (D) Negative Enthalpy and positive Entropy
For the spontaneous reaction, the negative enthalpy and positive entropy is most likely.
As for spontaneous reaction the value of ΔG must be negative.
Hence, as per formula, ΔG = ΔH − TΔS, So, if ΔH and ΔS are negative and positive respectively then the value of the ΔG must be negative whatever the temperature.

Acetone is a very volatile solvent, it evaporates quickly.
The heat is absorbed from the surface.
This process is called a endothermic reaction.

Entropy of system is increasing and of surroundings decreasing.

Thermodynamics laws are about energy transformation of a process and feasibility of a process.

Hess's law of constant heat summation deals with the enthalpy change for a chemical reaction. The chemical reaction can involve any chemical change. It may include formation or transition.

Thermodynamics is not concerned with rate at which a reaction proceeds. The rate of reaction is dealt by kinetics.

Without atmosphere, earth will turn into a ball of ice.
It’s temperature will decrease due to absence of green house gases which trap the sun’s heat and keep the planet warm.

In cyclic process, the change in internal energy of a system over one complete cycle is always zero.

From the above options Work depends on the shift from one state to another.

Hydrogen is the most abundant element in the universe followed by Helium.

In an exothermic reaction, there is the decrease in enthalpy on passing from reactants to products.

The water at the top of the waterfall, falls and gains velocity.
The potential energy it has converts into kinetic energy.
When the water lands at the bottom, the kinetic energy converts into heat and hence the water is warmer at the bottom.

Hess law includes initial reactants and final products.

It is an endothermic process as heat is being absorbed.

The enthalpies of all elements in their standard states are zero.

Combustion is an oxidation reaction and during this reaction, heat is produced.
In this type of reaction, bonds are broken first and then new bonds may be created results in new material formation.
So, it is always an exothermic reaction.

If a closed reaction vessel is made of copper, it will work as closed system because in such system heat will be exchanged with the surroundings but no matter will exchange.

The enthalpy change for the overall process is the sum of the enthalpy change of the steps in the process.

The statement "The change of enthalpy of a chemical reaction is same whether the reaction takes place in one or several steps" is Hess’s law of constant heat summation.

Explanation: (D) by itself but it has now effect on how fast the reaction takes
A spontaneous reaction occurs by itself but it has no effect on how fast the reaction takes.
A spontaneous reaction may be very fast but another spontaneous reaction may be very slow.

In Peltier effect, heat loss and heat gain depends upon the direction of current.
A typical Peltier heat pump involves multiple junction in series in which direction of current is important.

When water freezes, the heat is transferred from system to the surroundings, thus entropy of system decreases but entropy of surroundings increases.

Internal energy is the hidden energy in a definite quantity of substance.

A spontaneous process is one that occurs on its own, without any energy used from the outside.
For example, a ball will roll down an incline; water will flow downhill; ice will melt into water; radioisotopes will decay; and iron will rust.
So all natural process are spontaneous.

Hess's law is based on law of conservation of energy.

A thermodynamic property is that, which is measurable and whose value describes the state of system. Out of the given quantities, heat doesn't describe the state of a system so it is not a thermodynamic property because a system doesn't contain heat but only can transfer heat.

Hess law deals with the heat changes in a chemical reaction.

Calorimeter is used to measure the heat absorbed or released by a reaction.
Centrifuge is used to separate precipitate from solution.
Barometer is used to measure pressure.
Balance is used to measure weight of a substance.
Battery is used to provide electricity.

Enthalpy of solution is the enthalpy change when one mole of solute dissolved in a specified amount of solvent.

A thermochemical equation cannot tell whether the reaction is feasible or not. Free energy data is required to determine whether the reaction is feasible or not.

Whether a reaction is endothermic or exothermic can be indicated by enthalpy change.
Enthalpy change is the difference in the enthalpy of products and the enthalpy of reactants.
A positive value of enthalpy change indicates endothermic reaction as the enthalpy of products is more than the enthalpy of reactants.
A negative value of enthalpy change indicates exothermic reaction as the enthalpy of products is less than the enthalpy of reactants.

The spontaneity of a reaction is indicated by gibbs free energy change.
A negative value of gibbs free energy change indicates the reaction is spontaneous.
A positive value of gibbs free energy change indicates the reaction is non spontaneous.
Zero value of gibbs free energy change indicates the reaction is at equilibrium.

Thermometer can be used in combination with a calorimeter to compare the specific heats of two substances.
Thermometer will measure the temperature.

In a exothermic reaction heat is released for stability of product with less energy.

According to Hess's law of constant heat summation, even if a chemical reaction takes place by several different routes, the change in enthalpy of the reaction will be same for all the routes.

For a spontaneous process the randomness of the molecules in the system increases so the entropy change of the system and surroundings must be positive.

Hess’s law is an application of first law of thermodynamics.

In thermodynamics, a reversible process is a process whose direction can be "reversed" by inducing infinitesimal changes to some property of the system via its surroundings, while not increasing entropy. Throughout the entire reversible process, the system is in thermodynamic equilibrium with its surroundings, which means that the hot body and surroundings are at same temperature.

Area under the curve is greater in irreversible compression than that of reversible compression.

Mixture of ice and water is a heterogeneous system because their chemical compositions are same but the physical properties are completely different.

Explanation:(D) Positive ΔS
Formula for Gibbs Free Energy is ΔG = ΔH − TΔS
Hence, Positive ΔS is multiplied by temperature in the equation that calculates free energy.
ΔS is entropy change.
ΔG is Gibbs Free Energy change.
ΔH is enthalpy change.

Gibbs free energy is an extensive propety.

Because these depend upon initial and final state and not on path.

Internal energy of a body depends upon the final and initial temperature of the body.
It does not depend upon the path an the process the body has undergoes.

The Seeback effect is the direct conversion of heat into electricity in which potential difference is needed to calculate the current density so the potential of two junctions must be known.
It has nothing to do with neutral temperature.

Isothermal processes are necessarily slow as they require heat transfer to remain at the same temperature which is done by being in thermal equilibrium with some reservoir.
A process will be isothermal only if it happens on timescales larger than the timescale required for effective heat transfer.

Hint : Hess’s law states that, if an overall reaction takes place in several steps, its standard reaction enthalpy is the sum of the standard enthalpies of the intermediate reactions, at the same temperature.

Calorimetry is used to determine heat of the reaction.

Whenever a system absorbs heat from the surroundings or when we supply thermal energy to a system, the internal energy of the system increases.
The heat absorbed increases the kinetic energy of the molecules causing them to move randomly.

The enthalpy change for the overall process is the sum of the enthalpy change of the steps in the process.
This law is conservation of energy.

Hess's law is related to change in heat during a reaction.
It states that the total change in heat enthalpy during the complete course of reaction is same whether the change is brought in one step or in several steps by one method or other method.