Thermodynamics Activity

Explain the concept conveyed by the term 'enthalpy change of a reaction':

• The thermal energy released or absorbed during a chemical reaction

• The alteration in mass occurring as a result of the reaction

• The shift in entropy experienced throughout the reaction process

• The variation in volume observed throughout the reaction

Answer explanation

This process involves a change in the internal energy of the system, which in turn leads to a change in enthalpy. If the reaction absorbs heat from the surroundings (feels cold), it is endothermic, and the ΔH value is positive. Conversely, if the reaction releases heat into the surroundings (feels warm), it is exothermic, and the ΔH value is negative.This process involves a change in the internal energy of the system, which in turn leads to a change in enthalpy. If the reaction absorbs heat from the surroundings (feels cold), it is endothermic, and the ΔH value is positive. Conversely, if the reaction releases heat into the surroundings (feels warm), it is exothermic, and the ΔH value is negative.

A zero-order reaction is characterized by:

• A constant half-life

• Doubling the concentration doubles the rate

• The rate depends linearly on concentration 

• The rate is independent of reactant concentration

Answer explanation

A zero-order reaction is characterized by a reaction rate that is independent of the concentration of the reactants. In other words, the rate of the reaction remains constant over time, regardless of how much reactant is present. This is in contrast to first-order and second-order reactions, where the reaction rate is directly proportional to the concentration of one or more reactants.

Elucidate the definition of 'activation energy':

• The energy liberated or absorbed as a consequence of a reaction.

• The disparity in energy between the products and reactants.

• The energy essential for initiating a reaction.

• The alteration in energy under constant pressure conditions

Answer explanation

When reactant molecules collide, they need to possess a certain amount of energy to break the existing bonds and form new ones. This initial energy input required to initiate the reaction is the activation energy. It's often represented as Ea in chemical equations.

Activation energy is crucial because it determines the rate at which a reaction proceeds. Reactions with higher activation energies tend to proceed more slowly because fewer collisions between reactant molecules possess sufficient energy to overcome the energy barrier and initiate the reaction.

Define the distinctive features of a 'first-order reaction':

• The duration for half of the reactants to disappear remains constant.

• When the concentration is doubled, the reaction rate also doubles.

• The rate of the reaction varies directly with the concentration.

• The rate of the reaction remains unaffected by changes in reactant concentration.

Answer explanation

A first-order reaction is a type of chemical reaction where the rate of the reaction is directly proportional to the concentration of only one reactant. This means that the rate of the reaction depends on the concentration of the reactant raised to the power of 1. First-order reactions are characterized by several distinctive features:

1. Rate Equation: The rate equation for a first-order reaction is typically of the form:

   Rate = k[A]

   Where:

   • Rate is the rate of the reaction.

   • k is the rate constant, which remains constant at a given temperature.

   • [A] is the concentration of the reactant (usually in moles per liter or molarity).

2. Half-Life: First-order reactions exhibit a constant half-life. The half-life (t1/2) is the time required for the concentration of the reactant to decrease to half of its initial value. For a first-order reaction, the half-life is independe

A second-order reaction is characterized by:

• A linear relationship between concentration and rate

• The rate is proportional to the square of the concentration

• The rate is inversely proportional to the concentration

• The rate is independent of concentration

Answer explanation

second-order reaction is a type of chemical reaction where the rate of the reaction is proportional to the square of the concentration of one reactant, or the product of the concentrations of two reactants. Several distinctive features characterize second-order reactions:

1. Rate Equation: The rate equation for a second-order reaction can take one of two forms:

   • For a reaction involving one reactant: Rate = k[A]^2

   • For a reaction involving two reactants: Rate = k[A][B] Where:

   • Rate is the rate of the reaction.

   • k is the rate constant, which remains constant at a given temperature.

   • [A] and [B] are the concentrations of the reactants (usually in moles per liter or molarity).

What is the primary driving force for reactions at the molecular level?

• Electromagnetic force

• Gravitational force

• Nuclear force

• Molecular collisions

Answer explanation

The primary driving force for reactions at the molecular level is the tendency of molecules to attain a lower energy state, or greater stability. This driving force is governed by the second law of thermodynamics, which states that systems tend to move towards a state of higher entropy (disorder) and lower free energy.

At the molecular level, reactions occur because they lead to a more energetically favorable arrangement of atoms and molecules. This can involve the formation of stronger chemical bonds, the release of energy in the form of heat or light, or the increase in entropy of the system.

What is the effect of a catalyst on the rate of reaction?

• It increases the rate of reaction

• It decreases the rate of reaction

• It has no effect on the rate of reaction

• It stabilizes the products of the reaction

Answer explanation

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy.

The effect of a catalyst on the rate of reaction can be summarized as follows:

Lowering Activation Energy

Increased Reaction Rate

Unchanged Equilibrium Position

Reversible Reactions

Reusable

What does the first law of thermodynamics state?

• Energy cannot be created or destroyed

• Energy flows from hot to cold objects

• Entropy of the universe is always increasing

• Energy is conserved in a system

Answer explanation

The first law of thermodynamics, also known as the law of energy conservation, states that energy cannot be created or destroyed in an isolated system. Instead, it can only change forms or be transferred from one object to another. In other words, the total energy of a closed system remains constant over time.

Mathematically, the first law of thermodynamics can be expressed as:

ΔU = Q - W

Where:

• ΔU is the change in internal energy of the system.

• Q is the heat added to the system.

• W is the work done by the system.

This equation states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

How does a catalyst affect the reaction rate?

• By lowering the activation energy.

• By increasing the activation energy.

• By increasing the concentration of reactants.

• By decreasing the concentration of products.

Answer explanation

catalyst affects the reaction rate by providing an alternative reaction pathway with a lower activation energy. Here's how it works:

1. Lowering Activation Energy

2. Facilitating Reaction Steps: Catalysts can interact with reactant molecules to stabilize transition states or intermediate species

3. Increasing Collision Frequency

4. Enhancing Reaction Selectivity:favoring the formation of specific products over others.

5. Not Consumed in Reaction: Importantly, catalysts are not consumed in the reaction they catalyze.

Which statement best describes the first law of thermodynamics?

• Energy cannot be created or destroyed

• Energy flows from hot to cold objects

• Entropy of the universe is always increasing

• Energy is conserved in a system

Answer explanation