physical I (p1& 2) Flashcards
What is the definition of relative atomic mass (Ar)?
The relative atomic mass (Ar) of an element is the average mass of an atom of an element, compared to one-twelfth of the mass of an atom of carbon-12.
What is the ideal gas equation?
PV=nRT
What is the difference between an exothermic and an endothermic reaction?
- Exothermic reaction: Releases energy to the surroundings, usually as heat. (e.g., combustion, respiration)
- Endothermic reaction: Absorbs energy from the surroundings, usually as heat. (e.g., photosynthesis, thermal decomposition)
How is the rate of reaction defined?
The rate of reaction is the change in the concentration of a reactant or product per unit time. It can be measured in terms of the speed at which reactants are used up or products are formed.
What factors affect the rate of reaction?
- Temperature: Increasing temperature increases the rate.
- Concentration: Increasing the concentration of reactants increases the rate.
- Surface area: A larger surface area increases the rate.
- Catalysts: Catalysts increase the rate without being consumed in the reaction.
What is meant by activation energy?
Activation energy is the minimum energy required for reactants to collide with enough energy to react and form products.
What are the properties of ionic compounds?
- High melting and boiling points due to strong electrostatic forces.
- They conduct electricity when molten or in solution.
- They are usually soluble in water.
What is an acid and a base according to the Arrhenius theory?
- Acid: A substance that increases the concentration of hydrogen ions (H⁺) in solution.
- Base: A substance that increases the concentration of hydroxide ions (OH⁻) in solution.
What is pH?
pH is a measure of the acidity or alkalinity of a solution. It is calculated as the negative logarithm of the concentration of hydrogen ions:
pH=−log[H+]
What happens in a neutralization reaction?
HCl (aq)+NaOH (aq)→NaCl (aq)+H2O
Acid + base → salt + water
What is the process of distillation?
Distillation is a method of separating mixtures based on differences in boiling points. It involves heating the mixture to vaporize the component with the lower boiling point, then condensing the vapor back into liquid.
What is the difference between oxidation and reduction in terms of electron transfer?
- Oxidation: The loss of electrons.
- Reduction: The gain of electrons.
What is meant by dynamic equilibrium?
Dynamic equilibrium occurs in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of reactants and products remain constant over time.
What is Le Chatelier’s Principle?
Le Chatelier’s Principle states that if a system at equilibrium is disturbed by a change in temperature, pressure, or concentration, the system will shift to counteract the disturbance and restore equilibrium.
What is a mole in chemistry?
A mole is the amount of substance that contains exactly 6.022×10^23 entities (atoms, molecules, or ions). This number is known as Avogadro’s number.
What is the difference between a strong acid and a weak acid?
- Strong acid: Fully dissociates in water, releasing all its hydrogen ions (e.g., hydrochloric acid).
- Weak acid: Only partially dissociates in water, releasing some hydrogen ions (e.g., acetic acid).
What is the purpose of titration in chemistry?
Titration is a technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
What is the formula for calculating the energy change in a reaction?
ΔH=Energy of products−Energy of reactants
What is the difference between a saturated and an unsaturated solution?
- Saturated solution: A solution in which no more solute can dissolve at a given temperature.
- Unsaturated solution: A solution in which more solute can dissolve at a given temperature.
What is the rate of reaction?
The rate of reaction is the change in concentration of reactants or products per unit time. It is usually expressed in mol/dm³/s.
What is a rate equation?
A rate equation shows the relationship between the rate of reaction and the concentration of reactants. It is in the form:
Rate=k[A]^a [B] ^b
Where: k is the rate constant
[A] and [B] are the concentrations of reactants
a and b are the orders of reaction with respect to A and B.
What does the order of reaction tell you?
The order of reaction indicates how the rate of reaction is affected by the concentration of a reactant. It can be:
o Zero order: rate is independent of concentration.
o First order: rate is directly proportional to concentration.
o Second order: rate is proportional to the square of concentration.
What is the rate constant k?
The rate constant is a proportionality constant that links the rate of reaction to the concentrations of reactants. It is specific to a particular reaction at a given temperature.
What factors affect the rate of reaction?
The rate of reaction can be influenced by:
1. Concentration of reactants
2. Temperature
3. Surface area of solid reactants
4. Presence of a catalyst
What is collision theory?
Collision theory states that for a reaction to occur, particles must collide with sufficient energy (activation energy) and in the correct orientation.
What is activation energy?
Activation energy is the minimum energy required for a successful collision to occur and for the reactants to be converted into products.
What does the Maxwell-Boltzmann distribution show?
X axis: energy
Y axis: number of molecules
The Maxwell-Boltzmann distribution shows the distribution of energies among particles in a sample. As temperature increases, the peak of the distribution shifts to higher energies, and more particles have energy greater than or equal to the activation energy.
How does temperature affect the rate of reaction?
Increasing temperature increases the rate of reaction because it:
o Increases the number of particles with energy greater than the activation energy.
o Increases the frequency of collisions.
What is a catalyst?
A catalyst is a substance that increases the rate of a reaction by lowering the activation energy by providing an alternative pathway. It is not consumed in the reaction.
What does a zero-order reaction mean?
In a zero-order reaction, the rate is independent of the concentration of the reactant. The rate law is: Rate=k.
What does a first-order reaction mean?
A first-order reaction is a chemical reaction in which the rate of the reaction is directly proportional to the concentration of the reactants.
What is the rate-determining step?
The rate-determining step is the slowest step in a reaction mechanism, which controls the overall rate of the reaction.
What are some methods for measuring the rate of reaction?
Common methods include:
1. Measuring the volume of gas produced.
2. Monitoring the change in mass.
3. Measuring the change in color (using a colorimeter).
4. Monitoring the change in pH.
What is oxidation?
Oxidation is the process in which an atom or ion loses electrons. It is often associated with an increase in oxidation state.
What is reduction?
Reduction is the process in which an atom or ion gains electrons. It is often associated with a decrease in oxidation state.
What is a redox reaction?
A redox (reduction-oxidation) reaction involves both oxidation and reduction processes occurring simultaneously. One species is oxidized (loses electrons), and another is reduced (gains electrons).
What is a disproportionation reaction
When an element is both reduced and oxidised in the same reaction
how do van der waals forces arrise
there is rando movement of electrons in molecules bond casuing it to have a temproy dipole which is the induced on neighbouring bonds causing a delta negative and dleta positive at the end of the molecule
why do solid halides form different products with concerntrated sulfuric acid
the halides have different reducing powers so their ability to reduce concertrated sulfuric acid varies
2HI → I2 + H2
what would the apperence of the contents be
purple gas would form then turn colourless
a black solid would form
Explain why sigma bonds are stronger than pie bonds
The pie bond is a p orbital on sideways overlapping above and below the carbon atom restricting movement
Sigma bonds are end to end overlapping a p orbital
Do ionic compounds conduct electricity
Not when they are a solid only when they are molten or dissolved to they’re ions are free to move
5 electron pairs around central atom
trigonal bipyramid
Are alkenes soluble in water?
no they don’t form H bonds
Are carboxylic acids strong or weak acids?
Weak
Define dynamic equilibrium in a closed system.
- rate of forward reaction = rate of back reaction
- concentrations of products and reactants remain constant
Define mean bond enthalpy. (3)
- energy required
- to break a particular covalent bond
- averaged over a range of compounds
Describe giant metallic structure and bonding
- giant metallic structure
- strong electrostatic attraction between lattices of cations and sea of delocalised electrons
- lots of energy required to overcome strong metallic bonding
Describe ionic bonding.
- giant ionic structure
- strong electrostatic attraction between oppositely charged positive and negative ions in lattices
- lots of energy required to break many strong ionic bonds to melt the substance
How can percentage uncertainty be reduced?
- larger volume
- larger mass
How do you prepare a 250cm3 solution?
- weigh beaker
- add sample
- reweigh beaker
- calculate mass
- add deionised water
- stir until dissolved
- transfer to volumetric flask with washings
- make up to 250cm3
- invert flask 3 times to mix contents
How do you separate liquids in a mixture?
- fractional distillation
Name a drying agent.
- anhydrous calcium chloride
- dessicant
State Hess’s Law
- enthalpy change of a chemical reaction
- is independent of the route taken
Why can yield be lower than 100%?
- impure reactants
- side reactions
- evaporations
- gases/solids remain dissolved
- gases escape
- product lost during transfers, purification and washing
Why is ice less dense than water and why is this important?
- in water, H bonds constantly break and reform
- in ice, H2O molecules are held in place by H bonds
- molecules are less densely packed
- means that ice forms on top of and floats on oceans so fish can survive
Why would yield be greater than 100%?
- product is not dry
- water is present
or
- [specific] impurities present in product
