M5Chem 1stSem Final Calc of Rate of Rxn,Collision,Endo&Exo,FreeE

Types of Rate

The average rate of reaction and the instantaneous rate of reaction are both ways to measure how fast a chemical reaction occurs, but they differ in how they are calculated and what they represent.

Key terms:

• A chemical reaction is a process in which substances, called reactants, undergo a transformation to form new substances, called products. During a chemical reaction, the bonds between atoms in the reactants are broken, and new bonds are formed to create the products. This process involves changes in the chemical composition and properties of the substances involved.

• Concentration refers to the amount of a substance (solute) present in a certain volume of a solution or mixture. It indicates how much of the substance is dissolved or dispersed in a given amount of solvent or total mixture.
  
  

Average Rate of Reaction:

• The average rate of reaction is calculated over a specific time interval. It is the change in concentration of a reactant or product divided by the time over which the change occurs.

• Instantaneous Rate of Reaction:

  • The instantaneous rate of reaction is the rate at a specific moment in time. It is essentially the slope of the concentration vs. time curve at any given point.

  • To find the instantaneous rate, you take the derivative of the concentration with respect to time.

​Expressing Rates of Change

• Rate: The ratio between two related quantities expressed in different units

  • Many describe how much something changes over time (ex: Speed is distance/time)

• Reaction Rate: The rate at which the reactants of a chemical reaction form the product​

  • Written in terms of a concentration [X]/t

  • Rate can be negative for a reactant or positive for a product

​Expressing Rates of Change

• To keep things simple, chemists use a single rate of reaction that is always positive based on the stoichiometry of the reaction

  • Take a typical reaction with reactants A & B and Product C

    • xA + yB → zC

Experience Chemistry | Lesson 12.1

​Calculating Reaction Rates

• Hydrogen and Iodine gas react to form hydrogen iodide, as shown in the equation H₂ + I₂ → 2HI. Suppose you are given a time interval from t₁=10 sec and t₂=20 sec where the change in H₂ concentration from 0.210 mol/L to 0.185 mol/L. Calculate the average reaction rate in that period

  • Step 1: Identify your knonws

    • [H₁] =0.210 mol/L

    • ​[H₂] =0.185 mol/L

    • t₁=10

    • t₂=20

    • x=1, y=1, z=2

Experience Chemistry | Lesson 12.1

​Calculating Reaction Rates

• Hydrogen and Iodine gas react to form hydrogen iodide, as shown in the equation H₂ + I₂ → 2HI. Suppose you are given a time interval from t₁=10 sec and t₂=20 sec where the change in H₂ concentration from 0.210 mol/L to 0.185 mol/L. Calculate the average reaction rate in that period.

  • Step 2: Substitute your knowns into the equation

    • ΔH=0.185-0.210=-0.025

    • Δt=20-10=10

    • x=1, y=1, z=2

Experience Chemistry | Lesson 12.1

​Calculating Reaction Rates

• For the same reaction H₂ + I₂ → 2HI. You are given a product concentration of 0.180 mol/L at a time of 15 seconds and a concentration of 0.205 mol/L at a time of 20 seconds. Calculate the average reaction rate for the time interval.

  • Step 2: Substitute your knowns into the equation

    • ΔHI=0.205-0.0180= 0.025

    • Δt=20-15=5

    • x=1, y=1, z=2

Experience Chemistry | Lesson 12.1

​Expressing Rates of Change

Multiple Choice

It is a process in which substances, called reactants, undergo a transformation to form new substances, called products.

• Average Rate of Reaction

• Chemical Reaction

• Instantaneous Rate of Reaction

• Concentration

Multiple Choice

It indicates how much of the substance is dissolved or dispersed in a given amount of solvent or total mixture.

• Average Rate of Reaction

• Chemical Reaction

• Instantaneous Rate of Reaction

• Concentration

Multiple Choice

It is the change in concentration of a reactant or product divided by the time over which the change occurs.

• Average Rate of Reaction

• Instantaneous Rate of Reaction

• Instantaneous Rate of Reaction

• Average Concentration of Reaction

Multiple Choice

It is the rate at a specific moment in time.

• Average Rate of Reaction

• Instantaneous Rate of Reaction

• Instantaneous Concentration of Reaction

• Average Concentration of Reaction

Chemical Kinetics

Objectives

In this topic you will

• Define chemical kinetics and collision theory.

• Identify ways to increase the rate of a chemical reaction.

Chemical kinetics is the study of

• the rates at which chemical reactions occur and

• the factors that affect those rates.

Chemical kinetics

Collision theory is a key concept in chemical kinetics that explains how chemical reactions occur at the molecular level.

Collision Theory

Collision theory states that for a reaction to be occur, the reacting molecules

• must collide with each other

• with sufficient energy (the activation energy) and

• in the proper orientation. 

​If all three occur, a collision will be successful (fruitful) and a chemical reaction will occur.

Factors Affecting Reaction Rate

The collision theory also helps to explain how factors such as temperature, pressure, concentration, and the presence of a catalyst can affect the rate of a chemical reaction by influencing the frequency and effectiveness of molecular collisions.

​On the following slides we will look at each of these factors.

Increasing the temperature of a reaction increases the rate of the reaction.

Remember that temperature is a measure in the kinetic energy of a substance. An increase in temperature results in an increase in the average kinetic energy of the particles in the reaction mixture. This leads to more energetic and frequent collisions between the reactant molecules.

1.Temperature

Increasing the temperature increases reaction rate because:

• Collisions happen more frequently.

• When they collide, more particles have sufficient energy to overcome the activation energy barrier.

2.Surface Area

When a solid reactant is crushed into smaller particles, its total surface area increases. As a result, the increased surface area of the smaller particles allows more of the reactant to come into contact with the other reactants or the solvent (if present). This in turn increases the frequency of collisions between the reactant particles. As a result, the reaction occurs faster when the solid reactant is crushed into smaller particles.

Increasing Surface Area Increases Reaction Rate

• Decrease in particle size increases SA.

• More reactant can come into contact with other reactants.

3.Volume

Remember that Boyles Law tells us that decreasing the volume increases the pressure of a gas. When we decrease the volume of a gaseous system the molecules are forced closer together and they collide with each other more frequently. This increase in pressure increases the frequency of collisions between the reacting molecules. Thus decreasing the volume of a gaseous system leads to an increase in the rate of the reaction.

Decrease Volume increases Rate:

• decrease volume increases pressure

• increases frequency of collisions

4.Concentration

In an aqueous system, increasing the concentration of a reactant increases the number of particles of that reactant in a given volume of the reaction mixture. Increasing the concentration of an aqueous reactant leads to a higher frequency of collisions between the reactant particles and the other reactants or products in the reaction mixture. As a result, the rate of the reaction increases.

Increased concentration

• increases particles in the space

• increases frequency of collisions.

5.Catalyst

A catalyst increases the rate of a chemical reaction by lowering the activation energy needed for the reaction to occur. It can do this in two ways.

• May provide an alternative pathway with a lower activation energy than the original pathway, or

• A catalyst may physically orient the particles properly requiring less energy to react.

You may remember from biology that enzymes are important biological catalysts. However, catalysts also occur in daily life outside of living organisms. One example of such catalysts is the catalytic converter, which is used in the exhaust systems of vehicles to reduce harmful emissions.

Multiple Choice

________ is a key concept in chemical kinetics that explains how chemical reactions occur at the molecular level.

• Average reaction rate

• Reaction Rate

• Collision theory

• Chemical kinetics

Multiple Select

Collision theory states that for a reaction to be occur, the reacting molecules :

• must collide with each other

• with sufficient energy (the activation energy)

• in the proper orientation.

• Chemical kinetics

Multiple Choice

Increasing the temperature of a reaction increases the rate of the reaction.

• True

• False

• Maybe

• Can't determine

Multiple Choice

the reaction occurs slower when the solid reactant is crushed into smaller particles.

• True

• False

• Maybe

• Can't determine

Multiple Choice

Decreasing the volume of a gaseous system leads to a decrease in the rate of the reaction.

• True

• False

• Maybe

• Can't determine

Multiple Choice

Increasing the concentration of an aqueous reactant leads to a higher frequency of collisions between the reactant particles and the other reactants or products in the reaction mixture. As a result, the rate of the reaction increases.

• True

• False

• Maybe

• Can't determine

Multiple Choice

A catalyst increases the rate of a chemical reaction by lowering the activation energy needed for the reaction to occur.

• True

• False

• Maybe

• Can't determine

Write your answers in your notebook.​
PartI
1.It is a process in which substances, called reactants, undergo a transformation to form new substances, called products.
2.It is the change in concentration of a reactant or product divided by the time over which the change occurs.
3.It is the rate at a specific moment in time.
4-8. List the 5 factors affecting reaction rate.
9-10. Balance this equation:
H₂ + I₂ → HI
Part II
1. Hydrogen and Iodine gas react to form hydrogen iodide, as shown in the equation H₂ + I₂ → 2HI. Suppose you are given a time interval from t₁=10 sec and t₂=20 sec where the change in H₂ concentration from 0.210 mol/L to 0.185 mol/L. Calculate the average reaction rate in that period.
2.For the same reaction H₂ + I₂ → 2HI. You are given a product concentration of 0.180 mol/L at a time of 15 seconds and a concentration of 0.205 mol/L at a time of 20 seconds. Calculate the average reaction rate for the time interval.

Endothermic and Exothermic Reactions

​Enthalpy change (ΔH) is the heat absorbed or released by a system during a process, typically a chemical reaction, under constant pressure.

​

​

Multiple Choice

What is an exothermic reaction?

• heat energy is given out to the surroundings

• heat energy is taken into the substance

• no energy is given out

Poll

Exothermic reactions give out heat energy to the surroundings?

• True

• False

Multiple Select

An example of an exothermic reaction is? Pick as many which you think apply?

• rusting nail

• neutralisation

• acid and alkali

• burning magnesium

• combustion

Multiple Choice

What happens to the temperature in an exothermic reaction?

• it stays the same

• the temperature decreases

• the temperature increases

Multiple Choice

Which of the following process is exothermic?

• Candle melting

• A puddle evaporating

• Dry ice (solid carbon dioxide) subliming to form gaseous carbon dioxide

• Water freezing to form ice

Multiple Choice

What is an example of exothermic?

• firework

• ice pack

• coal

• wood

Multiple Choice

What type of reaction occurs in a hand warmer?

• exothermic

• endothermic

Multiple Choice

What type of reaction is shown in the photo?

• Exothermic
• Isothermic
• Endothermic
• None of the  above

Multiple Choice

If a chemical reaction is EXOTHERMIC, the temperature would....

• Stay the same
• Increase
• Decrease

Multiple Choice

In an exothermic reaction, heat is ...

• taken in
• given out

Multiple Choice

Endothermic means energy _______.

• absorbed

• released

Multiple Choice

____ reactions usually feel cold.

• endothermic

• exothermic

Multiple Choice

Is photosnythesis an Exothermic or an Endothermic reaction?

• Endothermic

• Exothermic

Multiple Choice

Baking bread and cooking an egg are examples of....?

• Endothermic processes
• Exothermic processess
• None of these 

Multiple Choice

A student mixed two chemicals to allow them to react. The temperature before the reaction was 25 ° C. The temperature after the reaction was 18° C. Which of the following is true?

• The temperature changed

• It is an endothermic reaction

• It is an exothermic reaction

Multiple Choice

In an endothermic reaction, heat is ...

• taken in

• given out

Equilibrium

​Changes in the concentrations of reactants (A and B) and products (C and D) as a system approaches equilibrium.
Only A and B are present at the beginning of the reaction.

​Equilibrium constant The ratio of product concentrations to reactant concentrations (with exponents that depend on the coefficients of the balanced equation).

​

​Entropy

Write your answer in your notebook.​
1.In an exothermic reaction, heat is ___________.
2.In an endothermic reaction, heat is ___________.
3. Calculate the Equilibrium constant.

​4.Calculate the Free Energy.