chemistry C3 Flashcards
Q: What is the law of conservation of mass?
A: The law of conservation of mass states that no atoms are lost or made in a chemical reaction. Therefore, no mass is lost or made.
Q: What must be true about the mass of reactants and products in a chemical reaction according to the law of conservation of mass?
A: The mass of the products at the end of a reaction must equal the mass of the reactants at the start.
Q: How do you balance a symbol equation?
A: You balance a symbol equation by ensuring the same number of atoms of each element are present on both sides. You can add numbers in front of chemical formulae as multipliers, but never change the numbers within a formula.
Q: What is relative atomic mass (Ar)?
A: The relative atomic mass (Ar) of an element is its average atomic mass.
Q: How do you calculate the relative formula mass (Mr) of a compound?
A: The Mr of a compound is found by adding up the relative atomic masses (Ar) of all the atoms in the compound. For example, the Mr of CO2 is 12 (C) + 16×2 (O) = 44.
Q: What is the relationship between Ar and the mass number of an element?
A: The Ar of an element is the same as its mass number, which is shown in the periodic table.
Q: What happens in a non-enclosed system during a chemical reaction?
A: In a non-enclosed system, reactants from the environment can enter, and products, usually gases, can escape into the environment.
Q: Why might the mass of products seem greater than the mass of reactants in a non-enclosed system?
A: The mass of products may seem greater if one of the reactants is a gas from the air, like oxygen reacting with a metal. The mass of the oxygen is not initially included in the reactants but is part of the product (metal oxide).
Q: Why might the mass of products seem less than the mass of reactants?
A: The mass of products may seem less if one of the products is a gas that escapes into the environment, like carbon dioxide from the decomposition of a metal carbonate.
Q: What is uncertainty in an experiment?
A: Uncertainty is the possibility that the measurements made in an experiment could be wrong. It can be estimated using the range or by plotting results on a graph.
Q: What does a range bar on a graph represent?
A: A range bar on a graph shows the uncertainty by indicating the range of results. A longer range bar indicates a higher uncertainty.
Q: What is a mole in terms of particles?
A: A mole contains 6.02 × 10²³ particles, known as the Avogadro constant. This number is the same regardless of the type of particle.
Q: How is the mass of 1 mole of a substance related to its Mr?
A: The mass of 1 mole of a substance in grams is the same as its relative formula mass (Mr).
Q: How do you calculate the number of moles from mass?
A: To calculate the number of moles, divide the mass of the substance (in grams) by its relative formula mass (Mr).
Q: What is the limiting reactant in a chemical reaction?
A: The limiting reactant is the substance that is completely used up first, limiting the amount of products that can be formed.
Q: What are excess reactants?
A: Excess reactants are substances that remain after the limiting reactant has been completely used up in a chemical reaction.
Q: How is the maximum possible amount of product determined?
A: The maximum possible amount of product is determined by the amount of the limiting reactant.
Q: What is concentration in chemistry?
A: Concentration is a measure of how much solute is dissolved in a certain volume of solution.
Q: How is concentration measured?
A: Concentration can be measured in grams per dm³ (g/dm³) or moles per dm³ (mol/dm³).
Q: What is yield in a chemical reaction?
A: Yield is the amount of product that is produced in a reaction.
Q: What is the difference between actual yield and maximum theoretical yield?
A: The maximum theoretical yield is the maximum amount of product that could form, while the actual yield is the amount actually produced in the experiment.
Q: What is atom economy?
A: Atom economy is the measure of how much of the starting materials in a chemical reaction end up as useful products.
Q: Why are reactions with high atom economies preferred?
A: Reactions with high atom economies are preferred because they produce more useful products with fewer wasted materials, making them better for profits and the environment.
Q: What factors affect the choice of reaction for a product?
A: Factors include yield, equilibrium position, reaction rate, and the usefulness of by-products.
Q: What is the importance of atom economy for sustainable development?
A: High atom economy reduces waste and pollution, making reactions more sustainable and environmentally friendly.
Q: How does concentration affect the volume of a gas produced in a reaction?
A: At the same temperature and pressure, equal amounts of different gases in moles occupy the same volume.
Q: What is the volume of 1 mole of gas at room temperature and pressure (RTP)?
A: At room temperature (20°C) and pressure (1 atm), 1 mole of any gas occupies 24 dm³.
Q: How can the volume of one gas be calculated in a reaction involving gases?
A: The volume of one gas can be calculated if you know the volumes of other gases involved in the reaction, using the molar ratios from the balanced equation.
example of a balanced equation (flip)
2Na + Cl2 = 2NaCl
what do you need to do to balance this equation?
O2 + H2 = H(little 2)O
add a 2 infront of the H in the reaction as it acts as a multiplier for the oxygen you now need to add another 2 infront of the H in the reaction to balance it out making
O2 + 2H2 = 2H(little 2)O
revison card (flip)
Equations cant be balanced by changing the little numbers because it makes it a diffrent chemical for example to balance the question for water you cant put in little 2s as it makes water into hydrigen peroxide(H(little 2)O(little 2))- this is what you CANT do > O2 + H2 = H(little 2)O(little 2)
you HAVE to use big numbers
revision card (flip)
the law of conservation of mass says no atoms are lost/made in a chemical reaction, so in a balancede equation the sum of M(little R)s of the products equals the sum of theM(little R)s of the reactants
For example you can show mass is conserved in 2 steps
- add up the relative forula of the reactants
(the Mr - little number ontop of the big number in the periodic table)
- you then add up the relative formula masses of the products (what the reaction is creating ) basically do the same thing before just with the other numbers
revision card (flip)
theres always a chance mesurements in an experiment could be wrong this is known as uncertainty this can be tested (roughly) using the range
uncertanity is range/2
a vertical line called a range bar can be drawn through each set of results to show the range and estimate the uncertainty - the longer the bar the higher the uncertainty
revision card (flip)
if you know the mass of a substance you can use the Mr to calculate the amount of moles it makes
moles = mass/Mr
this can be rearranged to find the mass in grams of a substance
mass=molesxMr
revision card (flip)
chemical equations can be described in terms of moles
the multipliers in front of the chemical formulae show the number of moles, if there is no multiplier before a formula the number of moles of that substance is 1
this means that balanced symbol equations can be used to calcaulate the mass of a reactant or product
can balanced equations be used to find the mass of a substance given the mass of another in a reaction
yes
for example
you can find the mass of hydrogen wirh 142g of chlorine
Mr of Cl2 = 35.5x2 = 71
mass of Cl2 = 142g
moles = mass/Mr
moles of Cl2 = 142/71 = 2 mol
then calculate how many mmoles of hydrogen react per mole of chlorine my looking at the symbol equation
1H2 + 1Cl2 = 2HCL
next how many moles of hydrogen were used up in the reaction - do this by multiplying the awnsers from the last 2 steps tg
moles of H2 = 2 x 1 = 2
then you can calculate the mass of hydrogen
Mr of H = 1x2=2
moles of H2 = 2mol
(mass=molesxMr)
mass of H2 = 2x2=4g
equation for mass moles and Mr
mass=molesxMr
triangle
mass ------------------ moles | Mr
equation for atom economy
percentage atom economy = (Mr of desired product / sum of Mr of all reactants ) x 100
atom economy is a measure of the amount of starting materials that end up in the final product
reactions with a high atom economy are usually ,more sustainable - they conserve earth reacources
equation for percentage yeild
percentage yeild = (actaul mass of product produced / maxiumum theoretical mass ) x 100
P=A/T x 100
why is there not 100% yeild
-the reactants form unexpected products
-some of the products may be lost in transferring reaction
-the reaction doesnt go to completion as it is reverible
-reactants may improve
