## SI Unit for Mass

Molly Posta 1H
Posts: 36
Joined: Wed Sep 30, 2020 10:05 pm

### SI Unit for Mass

Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some use g?

Wil Chai 3H
Posts: 40
Joined: Wed Sep 30, 2020 9:55 pm
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### Re: SI Unit for Mass

The equations that involve joules as a unit require you to use kg, because 1 J = 1 kg m^2 s^-2 . It's important to note also that all equations with Planck's constant require kg, since h = 6.626x10^-34 J*s.
Last edited by Wil Chai 3H on Wed Oct 28, 2020 5:21 pm, edited 1 time in total.

kateraelDis2F
Posts: 48
Joined: Wed Sep 30, 2020 9:54 pm

### Re: SI Unit for Mass

Whenever you use DeBroglie, you always want mass in kg. Whether that be the mass of an electron or something else.

Posts: 83
Joined: Wed Sep 30, 2020 9:32 pm
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### Re: SI Unit for Mass

Most of the energy equations require kg because Joules = kg⋅m^2⋅s^−2, so you need to use kg to make sure the units cancel. In converting from mass to moles, you just use the molar mass in grams, but otherwise, kg it typically used as it is the SI unit for mass.

Hope this helps!

Nathan Lao 2B
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Joined: Wed Sep 30, 2020 9:40 pm
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### Re: SI Unit for Mass

It's probably easier to use kg instead of grams since Planck's constant is given as 6.626x10^/34 kg m^2 s^-1. Cancelling units is pretty easy from there.

Bai Rong Lin 3I
Posts: 36
Joined: Wed Sep 30, 2020 9:54 pm

### Re: SI Unit for Mass

Molly Posta 1H wrote:Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some use g?

It is based on what type of constant you are using and its units I believe, but the majority of the time kg is being used in these constants!

ShinwooKim_3E
Posts: 40
Joined: Wed Sep 30, 2020 10:00 pm

### Re: SI Unit for Mass

Molly Posta 1H wrote:Out of all the equations we've used so far in units 1 and 2, should mass always be in kg? I've been using g for mass for most of my work, but I noticed while reviewing the De Broglie equation that mass needs to be converted into kg for this example. Do some equations require mass in kg while some use g?

We should always leave mass in kg when using the De Broglie equation (it's different when talking about stoichiometry or mass measurements of compounds, then we use g)

Kathy_Li_3J
Posts: 40
Joined: Wed Sep 30, 2020 9:31 pm

### Re: SI Unit for Mass

Hi! The SI unit for Mass is kilograms, so I would just assume that the equation uses kilograms unless otherwise stated (e.g. the final units has g instead of kg).

Gicelle Rubin 1E
Posts: 41
Joined: Fri Oct 02, 2020 12:16 am

### Re: SI Unit for Mass

Hi! I am pretty sure mass has to be in kg. In examples where I'm given grams, I convert to kg before using any equation.