# CH1 - Chemistry Equations

Because Chemistry isn't difficult enough to revise for anyway, without the addition of equations.

• Created by: Katy **
• Created on: 19-05-15 11:33

## Determination of enthalpy change of calorimetry

= -m x c x change in temperature/moles

-m is the mass of substance absorbed (usually water)

c is the specific heat capacity (usually 4.12kJ)

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## Rate of Reaction

= change in concentration of product or reactants / time

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## Empirical Formulae

1. moles = mass / Ar

2. divide by the smallest

3. apply to the atom

e.g.

Al - 6.75/27 = 0.25

Cl - 26.63/35.5 = 0.75

0.25/0.25 = 1

0.75/0.25 = 3

AlCl3

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## Calculating mass of reactants or products formed

1. calculate moles of what know

2. use equation to work out what know-finding ratio

3. calculate what trying to find

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## Molecular Formulae

Mr / empirical mass = [ANS]

[ANS] x empirical formulae

e.g.

AlCl3

Mr - 267

Empirical mass - 133.5

267/133.5 = 2

AlCl3 x 2 = 2AlCl3

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## Molar volume of gas

= volume of gas / 24dm3

e.g.

6g of Nitrogen

6/24 = 0.25

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## Gas Laws

(P x V / T) = (P2 x V2 / T2)

temperature must be in K = 'c + 273

e.g.

(100x400/473) = (P2x50/473)

P2 = (100x400/50)

P2 = 80kPa

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## Percentage Yield

= actual yeild / theoretical yield

e.g.

theoretical yield is just Mr of each atom

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## Percentage of Atom Economy

= mass of useful / total mass of reactants x100

1. calculate the Mr of each atom

2. calculate the total mass for reactants (include the front numbers)

3. calculate the total mass of wanted products (including the front numbers)

4. apply to formulae

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## Relative Atomic Mass

= abundance of each isotope x peak / 100 or total abundance

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## Hess' Law

delta H = delta H1 + delta H2

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## Enthalpy change using average bond enthalpy

= energy of bonds broken - energy of bonds made

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## Percentage Composition

= Ar of atoms intrested / Mr x100

e.g.

NH4Cl

N% = 14/53.5 x100

N% = 26.2%

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## Moles

moles = mass / Mr

moles = concentration x volume /1000

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