topic 6 -The rate and extent of chemical change

Question 1

How is rate of reaction calculated?

Answer 1

almost if reactant used or product formed
———————————————————-
time

moles of reactant used or product formed
————————————————————
time

Question 2

what are the various units for rate of reaction?

Answer 2

g/s cm3/s mol/s

Question 3

name the three common ways of measuring rate of reaction

Answer 3

Loss in mass of reactants
Volume of gas produced
Time for a solution to become opaque

Question 4

Describe measuring the rate by monitoring mass loss

Answer 4

place a reaction flask on a balance. In these reactions a gas is given off, so record the decrease in mass in time intervals. Plot a graph of mass versus time. 

Question 5

describe measuring the rate by monitoring the volume of gas

Answer 5

Connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals

Plot graph of volume versus time

Question 6

describe measuring the rate by monitoring the disappearance of a cross

Answer 6

take a piece of paper and mark a cross on it. Put the reaction flask on its cross. Mix the reagent and measure how long it takes for a cloudy mixture to conceal the cross

Question 7

How to find a rate of reaction at some time from a graph of amount of reactant versus time

Answer 7

pick a point corresponding to the time and find the tangent to the curb at this point

The tangent is the gradient of this grass. It tells you how fast a reaction proceeds at this point. The steep with the tangent light, the faster it is

Question 8

State five factors affecting the rate of chemical reaction

Answer 8

concentration of reactants
Pressure of gases
Surface area
Temperature
Catalysts

Question 9

What is the collision theory?

Answer 9

Chemical reactions can occur only when reacting particles collide with each other with sufficient energy

Question 10

describing and explain the effect of increasing temperature on the rate of reaction

Answer 10

T increases=faster reaction

as t increases, kinetic energy of particles increases also they move faster to the Collide more frequently

However, there is no straight line between right and temperature

Question 11

Describe and explain the effect of increasing concentration on the rate of reaction

Answer 11

conc increase = faster reactions
more reactants = more frequent reactions

Question 12

Describe and explain the effect of increasing pressure of a gas on the rate of reaction

Answer 12

Increasing the pressure of reacting gases is the same as increase in concentration. It increases the number of gas molecules in the same volume and so increases the frequency of collisions and therefore increases the rate of reaction.

Question 13

Describe and explain the effect of increasing surface area

Answer 13

If solid reactants are in smaller pieces, they have a greater surface area. Increasing the surface area of a solid reactant increases the frequency of collisions and so increases the rate of reaction.

Question 14

what is a catalyst and how does it work? How does it affect the reaction profile?

Answer 14

A catalyst changes the rate of reaction, but it’s not used up. It increases the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. The reaction profile for a catalyse reaction will have a lower maximum of the curve.

Question 15

What is an enzyme?

Answer 15

an enzyme is a molecule that acts as a catalyst in a biological system 

Question 16

What is a reversible reaction?

Answer 16

A reversible reaction occurs when the products of reaction can react backwards to produce the original reactants

Question 17

When is dynamic equilibrium reached?

Answer 17

In a close system, when the forward and reverse reactions occur at the same time and the concentrations of reactants and products remain constant

Question 18

Describe le chantelier principle

Answer 18

If a system is at equilibrium and change is made to any of the conditions, then the system responds to a counteract change and restore the equilibrium

Question 19

describe the effect of changing the concentration of reactant and product on the position of the equilibrium

Answer 19

If the concentration of one of the reactants are product is changed the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again. If the concentration of reactant is increased, more products will be formed until equilibrium is reached again. If the concentration of a product is decreased more reactant will react until equilibrium is reached again.

Question 20

Describe the effect of changing temperature on the position of the equilibrium

Answer 20

if the temperature of a system at equilibrium is increased; the relative amount of products are equilibrium increases for an endothermic reaction

The relative amount of products are equilibrium decreases for an exothermic reaction

Question 21

describe the effect of changing pressure on the position of the equilibrium

Answer 21

This applies to equilibrium that involves gas

An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules as shown by the simple equation for that reaction. A decrease in pressure causes the equilibrium position to shift towards the side with a larger number of molecules as showed by the symbol equation for that reaction. Pressure has no effect on reactions where the number of gas molecules are equal on both sides of the equation.

Question 22

Describe the effect of a catalyst on the position of the equilibrium

Answer 22

No effect it just speeds up both forward and backward reactions equally